JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter UniPHY Group iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

7 Sep 2011

Volume 135, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 135, 094501 (2011); http://dx.doi.org/10.1063/1.3624495 (8 pages)

Nina Verdal, Terrence J. Udovic, John J. Rush, Vitalie Stavila, Hui Wu, Wei Zhou, and Timothy Jenkins
Enlarge Image | Read More
Page 1 of 2 Pages Next Page | Jump to Page
back to top
RSS Feeds
FREE

Communication: Probable scenario of the liquid–liquid phase transition of SnI4

Kazuhiro Fuchizaki, Nozomu Hamaya, Takaki Hase, and Yoshinori Katayama

J. Chem. Phys. 135, 091101 (2011); http://dx.doi.org/10.1063/1.3637038 (4 pages)

Online Publication Date: 1 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have shown from in situ synchrotron x-ray diffraction measurements that there are two thermodynamically stable liquid forms of SnI4, depending on the pressure. Based on the liquid–liquid critical point scenario, our recent measurements suggest that the second critical point, if it exists, may be located in a region close to the point at which the melting curve of the crystalline phase abruptly breaks. This region is, unlike that of water, experimentally accessible with relative ease.
Show PACS
64.70.Ja Liquid-liquid transitions
64.70.dj Melting of specific substances
FREE

Communication: Theoretical exploration of Au++H2, D2, and HD reactive collisions

Anaís Dorta-Urra, Alexandre Zanchet, Octavio Roncero, Alfredo Aguado, and P. B. Armentrout

J. Chem. Phys. 135, 091102 (2011); http://dx.doi.org/10.1063/1.3635772 (4 pages)

Online Publication Date: 6 September 2011

Full Text: Read Online (HTML) | Download PDF


See Also: Publisher's Note

Show Abstract
A quasi-classical study of the endoergic Au+(1S) + H2(X1Σg+) → AuH+ (2Σ+) + H(2S) reaction, and isotopic variants, is performed to compare with recent experimental results [F. Li, C. S. Hinton, M. Citir, F. Liu, and P. B. Armentrout, J. Chem. Phys. 134, 024310 (2011)].10.1063/1.3514899 For this purpose, a new global potential energy surface has been developed based on multi-reference configuration interaction ab initio calculations. The quasi-classical trajectory results show a very good agreement with the experiments, showing the same trends for the different isotopic variants of the hydrogen molecule. It is also found that the total dissociation into three fragments, Au++H+H, is the dominant reaction channel for energies above the H2 dissociation energy. This results from a well in the entrance channel of the potential energy surface, which enhances the probability of H–Au–H insertion.
Show PACS
34.20.Gj Intermolecular and atom-molecule potentials and forces
34.50.Lf Chemical reactions
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
33.15.Fm Bond strengths, dissociation energies
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Dispersion energy evaluated by using locally projected occupied and excited molecular orbitals for molecular interaction

Suehiro Iwata

J. Chem. Phys. 135, 094101 (2011); http://dx.doi.org/10.1063/1.3629777 (12 pages) | Cited 1 time

Online Publication Date: 1 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The dispersion terms are evaluated with the perturbation theory based on the locally projected molecular orbitals. A series of model systems, including some of the S22 set, is examined, and the calculated binding energies are compared with the published results. The basis set dependence is also examined. The dispersion energy correction is evaluated by taking into account the double excitations only of the dispersion type electron configurations and is added to the 3rd order single excitation perturbation energy, which is a good approximation to the counterpoise (CP) corrected Hartree-Fock (HF) binding energy. The procedure is the approximate “CP corrected HF + D” method. It ensures that the evaluated binding energy is approximately free of the basis set superposition error without the CP procedure. If the augmented basis functions are used, the evaluated binding energies for the predominantly dispersion-bound systems, such as rare gas dimers and halogen bonded clusters, agree with those of the reference calculations within 1 kcal mol−1 (4 kJ mol−1). The limitation of the present method is also discussed.
Show PACS
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xp Perturbation theory
31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

A constrained approach to multiscale stochastic simulation of chemically reacting systems

Simon L. Cotter, Konstantinos C. Zygalakis, Ioannis G. Kevrekidis, and Radek Erban

J. Chem. Phys. 135, 094102 (2011); http://dx.doi.org/10.1063/1.3624333 (12 pages) | Cited 1 time

Online Publication Date: 1 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Stochastic simulation of coupled chemical reactions is often computationally intensive, especially if a chemical system contains reactions occurring on different time scales. In this paper, we introduce a multiscale methodology suitable to address this problem, assuming that the evolution of the slow species in the system is well approximated by a Langevin process. It is based on the conditional stochastic simulation algorithm (CSSA) which samples from the conditional distribution of the suitably defined fast variables, given values for the slow variables. In the constrained multiscale algorithm (CMA) a single realization of the CSSA is then used for each value of the slow variable to approximate the effective drift and diffusion terms, in a similar manner to the constrained mean-force computations in other applications such as molecular dynamics. We then show how using the ensuing Fokker-Planck equation approximation, we can in turn approximate average switching times in stochastic chemical systems.
Show PACS
82.20.Uv Stochastic theories of rate constants
05.10.Gg Stochastic analysis methods (Fokker-Planck, Langevin, etc.)
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Accurate predictions of the energetics of silicon compounds using the multireference correlation consistent composite approach

Gbenga A. Oyedepo, Charles Peterson, and Angela K. Wilson

J. Chem. Phys. 135, 094103 (2011); http://dx.doi.org/10.1063/1.3626838 (12 pages) | Cited 1 time

Online Publication Date: 1 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Theoretical studies, using the multireference correlation consistent composite approach (MR-ccCA), have been carried out on the ground and lowest lying spin-forbidden excited states of a series of silicon-containing systems. The MR-ccCA method is the multireference equivalent of the successful single reference ccCA method that has been shown to produce chemically accurate (within ±1.0 kcal mol−1 of reliable, well-established experiment) results. The percentage contributions of the SCF configurations to complete active space self-consistent field wave functions together with the Frobenius norm of the t1 vectors and related D1 diagnostics of the coupled-cluster single double wave function with the cc-pVTZ basis set have been utilized to illustrate the multi-configurational characteristics of the compounds considered. MR-ccCA incorporates additive terms to account for relativistic effects, atomic spin-orbit coupling, scalar relativistic effects, and core-valence correlation. MR-ccCA has been utilized to predict the atomization energies, enthalpies of formation, and the lowest energy spin-forbidden transitions for SinXm (2 ≤ n + m ≥ 3 where n ≠ 0 and X = B, C, N, Al, P), silicon hydrides, and analogous compounds of carbon. The energetics of small silicon aluminides and phosphorides are predicted for the first time.
Show PACS
31.15.xr Self-consistent-field methods
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
33.15.Fm Bond strengths, dissociation energies
82.60.Cx Enthalpies of combustion, reaction, and formation

Second-order perturbation theory with a density matrix renormalization group self-consistent field reference function: Theory and application to the study of chromium dimer

Yuki Kurashige and Takeshi Yanai

J. Chem. Phys. 135, 094104 (2011); http://dx.doi.org/10.1063/1.3629454 (9 pages) | Cited 2 times

Online Publication Date: 2 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a second-order perturbation theory based on a density matrix renormalization group self-consistent field (DMRG-SCF) reference function. The method reproduces the solution of the complete active space with second-order perturbation theory (CASPT2) when the DMRG reference function is represented by a sufficiently large number of renormalized many-body basis, thereby being named DMRG-CASPT2 method. The DMRG-SCF is able to describe non-dynamical correlation with large active space that is insurmountable to the conventional CASSCF method, while the second-order perturbation theory provides an efficient description of dynamical correlation effects. The capability of our implementation is demonstrated for an application to the potential energy curve of the chromium dimer, which is one of the most demanding multireference systems that require best electronic structure treatment for non-dynamical and dynamical correlation as well as large basis sets. The DMRG-CASPT2/cc-pwCV5Z calculations were performed with a large (3d double-shell) active space consisting of 28 orbitals. Our approach using large-size DMRG reference addressed the problems of why the dissociation energy is largely overestimated by CASPT2 with the small active space consisting of 12 orbitals (3d4s), and also is oversensitive to the choice of the zeroth-order Hamiltonian.
Show PACS
31.15.xp Perturbation theory
31.15.xr Self-consistent-field methods
31.50.-x Potential energy surfaces
33.15.Fm Bond strengths, dissociation energies
31.15.xh Group-theoretical methods

Long-range-corrected hybrids using a range-separated Perdew-Burke-Ernzerhof functional and random phase approximation correlation

Robert M. Irelan, Thomas M. Henderson, and Gustavo E. Scuseria

J. Chem. Phys. 135, 094105 (2011); http://dx.doi.org/10.1063/1.3630951 (7 pages)

Online Publication Date: 2 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We build on methods combining a short-range density functional approximation with a long-range random phase approximation [B. G. Janesko, T. M. Henderson, and G. E. Scuseria, J. Chem. Phys. 130, 081105 (2009)10.1063/1.3090814] or second-order screened exchange [J. Paier et al., J. Chem. Phys. 132, 094103 (2010)10.1063/1.3317437] by replacing the range-separated local density approximation functional with a range-separated generalized gradient approximation functional in the short range. We present benchmark results that show a marked improvement in the thermodynamic tests over the previous local density approximation-based methods while retaining those methods’ excellent performance in van der Waals interactions.
Show PACS
31.15.E- Density-functional theory
34.20.Gj Intermolecular and atom-molecule potentials and forces

Novel numerical method for calculating the pressure tensor in spherical coordinates for molecular systems

Takenobu Nakamura, Wataru Shinoda, and Tamio Ikeshoji

J. Chem. Phys. 135, 094106 (2011); http://dx.doi.org/10.1063/1.3626410 (10 pages) | Cited 2 times

Online Publication Date: 6 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We propose a novel method for computing the pressure tensor along the radial axis of a molecular system with spherical symmetry. The proposed method uses the slice averaged pressure to improve the numerical stability and precision significantly. Simplified expressions of the local pressure are derived for a conventional molecular force field including non-bond, bond stretching, angle bending, and torsion interactions; these expressions are advantageous in terms of the computational cost. We also discuss an algorithm to avoid numerical singularity. Finally, the method is successfully applied to three different molecular systems, i.e., a water droplet in oil, a spherical micelle, and a liposome.
Show PACS
61.20.Ja Computer simulation of liquid structure
61.25.Em Molecular liquids
68.03.Hj Liquid surface structure: measurements and simulations
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)
87.15.N- Properties of solutions of macromolecules

The spin-polarized extended Brueckner orbitals

A. V. Luzanov and O. V. Prezhdo

J. Chem. Phys. 135, 094107 (2011); http://dx.doi.org/10.1063/1.3629780 (14 pages)

Online Publication Date: 6 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Conventional natural and Brueckner orbitals (BOs) are rather frequently used for improving active orbital spaces in various configuration interaction (CI) approaches. However, the natural and Brueckner single-determinant models per se fail to give an adequate picture of highly correlated and quasidegenerate states such as open-shell singlet and dissociative states. We suggest the use of the spin-polarized extended BOs formally defining them in the same manner as in Löwdin's spin-extended Hartree-Fock method. Such BO orbitals turn out to be quite flexible and particularly useful for analyzing highly correlated electronic states. It is shown that the extended BOs always exist, unlike the usual unrestricted BOs. We discuss difficulties related to violation of size-consistency for spin projected determinant models. The working algorithm is proposed for computing BOs within the full CI and related complete active space methodology. The extended BOs are analyzed in terms of the special density-like matrices associated with spin-up and spin-down BO orbitals. From these density matrices, the corresponding spin-polarization diagrams are produced for effectively unpaired (essentially correlated) electrons. We illustrate the approach by calculations on cyclic hydrogen clusters (H4, H6, and H8), certain carbene diradicals and monoradicals, and low-lying excited states. The computations show that the BO spin-projected determinant provides a strong overlap with the multi-configurational state even for quasidegenerate states and bond breaking processes.
Show PACS
36.40.Cg Electronic and magnetic properties of clusters
33.15.Fm Bond strengths, dissociation energies
31.15.vq Electron correlation calculations for polyatomic molecules
31.15.xr Self-consistent-field methods

Hybrid coupled-cluster and perturbation method for extended systems of one-dimensional periodicity

Yu-ya Ohnishi and So Hirata

J. Chem. Phys. 135, 094108 (2011); http://dx.doi.org/10.1063/1.3629843 (10 pages)

Online Publication Date: 6 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A hybrid of the coupled-cluster singles and doubles (CCSD) and second-order Møller–Plesset perturbation (MP2) methods [M. Nooijen, J. Chem. Phys. 111, 10815 (1999)10.1063/1.480445; A. D. Bochevarov and C. D. Sherrill, ibid. 122, 234110 (2005); A. D. Bochevarov et al., ibid. 125, 054109 (2006)] is formulated and implemented for one-dimensional periodic extended systems, in which the excitation (T) amplitudes of active bands are determined iteratively by CCSD, while the T amplitudes of mixed active/inactive bands are held fixed at the first-order Møller–Plesset perturbation values. The occupied and virtual bands near the Fermi level, which can cause instability in MP2 when they are (quasi-)degenerate, are selected as active bands to be treated by CCSD, which can, in principle, resist such instability. Two contraction schemes of the T amplitudes (Contractions A and B) are considered. Contraction A is the one proposed for molecules and used also for extended systems because it is efficient for CCSD, but not necessarily so for the hybrid CCSD/MP2. Contraction B is introduced to be more optimally efficient for the hybrid CCSD/MP2 by maximizing the number of intermediate quantities made of the inactive T amplitudes and molecular integrals, which do not vary during CCSD iterations and are computed only once, stored, and reused. In an application to trans-polyacetylene, a smooth transition of the results of the hybrid CCSD/MP2 is observed toward those of CCSD and MP2 by increasing and decreasing, respectively, the number of active bands. With the smallest active space, the hybrid CCSD/MP2 with Contractions A and B achieves a speedup by a factor of 360 and 520, respectively, relative to CCSD. When all of the occupied bands and about half of the virtual bands are active, the hybrid CCSD/MP2 can recover 98% of the CCSD correlation energy or half of the difference between CCSD and MP2 at less than a tenth of the usual CCSD cost.
Show PACS
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory

Computer simulations of thermo-shrinking polyelectrolyte gels

Manuel Quesada-Pérez, José Guadalupe Ibarra-Armenta, and Alberto Martín-Molina

J. Chem. Phys. 135, 094109 (2011); http://dx.doi.org/10.1063/1.3632051 (10 pages)

Online Publication Date: 7 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this work, thermo-responsive polyelectrolyte gels have been simulated using polymer networks of diamond-like topology in the framework of the primitive model. Monte Carlo simulations were performed in the canonical ensemble and a wide collection of situations has been systematically analysed. Unlike previous studies, our model includes an effective solvent-mediated potential for the hydrophobic interaction between non-bonded polymer beads. This model predicts that the strength of the attractive hydrophobic forces increases with temperature, which plays a key role in the explanation of the thermo-shrinking behaviour of many real gels. Although this hydrophobic model is simple (and it could overestimate the interactions at high temperature), our simulation results qualitatively reproduce several features of the swelling behaviour of real gels and microgels reported by experimentalists. This agreement suggests that the effective solvent-mediated polymer-polymer interaction used here is a good candidate for hydrophobic interaction. In addition, our work shows that the functional form of the hydrophobic interaction has a profound influence on the swelling behaviour of polyelectrolyte gels. In particular, systems with weak hydrophobic forces exhibit discontinuous volume changes, whereas gels with strong hydrophobic forces do not show hallmarks of phase transitions, even for highly charged polyelectrolyte chains.
Show PACS
82.35.Rs Polyelectrolytes
82.45.Wx Polymers and organic materials in electrochemistry
82.70.Gg Gels and sols
61.25.hp Polymer swelling, cross linking
61.20.Ja Computer simulation of liquid structure
68.08.Bc Wetting
back to top Advanced Experimental Techniques

A method for the determination of speed-dependent semi-classical vector correlations from sliced image anisotropies

Michael P. Grubb, Michelle L. Warter, C. Daniel Freeman, Niclas A. West, Kelly M. Usakoski, Kurt M. Johnson, Jeffrey A. Bartz, and Simon W. North

J. Chem. Phys. 135, 094201 (2011); http://dx.doi.org/10.1063/1.3631343 (9 pages)

Online Publication Date: 6 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present analytical expressions relating the bipolar moment βQK(k1k2) parameters of Dixon to the measured anisotropy parameters of different pump/probe geometry sliced ion images. In the semi-classical limit, when there is no significant coherent contribution from multiple excited states to fragment angular momentum polarization, the anisotropy of the images alone is sufficient to extract the βQK(k1k2) parameters with no need to reference relative image intensities. The analysis of sliced images is advantageous since the anisotropy can be directly obtained from the image at any radius without the need for 3D-deconvolution, which is not applicable for most pump/probe geometries. This method is therefore ideally suited for systems which result in a broad distribution of fragment velocities. The bipolar moment parameters are obtained for NO2 dissociation at 355 nm using these equations, and are compared to the bipolar moment parameters obtained from a proven iterative fitting technique for crushed ion images. Additionally, the utility of these equations in extracting speed-dependent bipolar moments is demonstrated on the recently investigated NO3 system.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
31.15.xg Semiclassical methods
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Predicted thermochemistry and unimolecular kinetics of nitrous sulfide

Paul Marshall, Yide Gao, and Peter Glarborg

J. Chem. Phys. 135, 094301 (2011); http://dx.doi.org/10.1063/1.3628521 (6 pages)

Online Publication Date: 1 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The geometry of N2S was obtained at the CCSD(T)/aug-cc-pV(T + d)Z level of theory and energies with coupled-cluster single double triple (CCSD(T)) and basis sets up to aug-cc-pV(6 + d)Z. After correction for anharmonic zero-point energy, core-valence correlation, correlation up to CCSDT(Q) and relativistic effects, D0 for the N–S bond is estimated as 71.9 kJ mol−1, and the corresponding thermochemistry for N2S is ΔfH0∘ = 205.4  kJ   mol −1 and ΔfH298∘ = 202.6  kJ   mol −1 with an uncertainty of ±2.5 kJ mol−1. Using CCSD(T)/aug-cc-pV(T + d) theory the minimum energy crossing point between singlet and triplet potential energy curves is found at r(N–N) ≈ 1.105 Å and r(N–S) ≈ 2.232 Å, with an energy 72 kJ mol−1 above N2 + S(3P). Application of Troe's unimolecular formalism yields the low-pressure-limiting rate constant for dissociation of N2S k0 = 7.6 × 10−10 exp(−126 kJ mol−1/RT) cm3 molecule−1 s−1 over 700–2000 K. The estimated uncertainty is a factor of 4 arising from unknown parameters for energy transfer between N2S and Ar or N2 bath gas. The thermochemistry and kinetics were included in a mechanism for CO/H2/H2S oxidation and the conclusion is that little NO is produced via subsequent chemistry of NNS.
Show PACS
82.60.Cx Enthalpies of combustion, reaction, and formation
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Kh Potential energy surfaces for chemical reactions
82.33.Vx Reactions in flames, combustion, and explosions
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Db Transition state theory and statistical theories of rate constants

Comparative study of cluster Ag17Cu2 by instantaneous normal mode analysis and by isothermal Brownian-type molecular dynamics simulation

Ping-Han Tang, Ten-Ming Wu, Tsung-Wen Yen, S. K. Lai, and P. J. Hsu

J. Chem. Phys. 135, 094302 (2011); http://dx.doi.org/10.1063/1.3628669 (16 pages)

Online Publication Date: 1 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We perform isothermal Brownian-type molecular dynamics simulations to obtain the velocity autocorrelation function and its time Fourier-transformed power spectral density for the metallic cluster Ag17Cu2. The temperature dependences of these dynamical quantities from T = 0 to 1500 K were examined and across this temperature range the cluster melting temperature Tm, which we define to be the principal maximum position of the specific heat is determined. The instantaneous normal mode analysis is then used to dissect the cluster dynamics by calculating the vibrational instantaneous normal mode density of states and hence its frequency integrated value Ij which is an ensemble average of all vibrational projection operators for the jth atom in the cluster. In addition to comparing the results with simulation data, we look more closely at the entities Ij of all atoms using the point group symmetry and diagnose their temperature variations. We find that Ij exhibit features that may be used to deduce Tm, which turns out to agree very well with those inferred from the power spectral density and specific heat.
Show PACS
36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.xv Molecular dynamics and other numerical methods
33.20.Tp Vibrational analysis
33.15.Bh General molecular conformation and symmetry; stereochemistry

Comparative density functional theory and post-Hartree-Fock (CCSD, CASSCF) studies on the electronic structure of halogen nitrites ClONO and BrONO using quantum chemical topology

Slawomir Berski and Agnieszka J. Gordon

J. Chem. Phys. 135, 094303 (2011); http://dx.doi.org/10.1063/1.3624894 (13 pages)

Online Publication Date: 1 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper, the electronic structures of cis- and trans-ClONO and BrONO are studied at the CCSD/aug-cc-pVTZ, CASSCF(14,12)/aug-cc-pVTZ, and B3LYP/aug-cc-pVTZ computational levels. For the Cl–O bond, topological analysis of the electron density field, ρ(r), shows the prevalence of the shared-electron type bond (∇2ρ(3,−1) < 0). The Br–O bond, however, represents the closed-shell interaction (∇2ρ(3,−1) > 0). Topological analysis of the electron localization function, η(r), and electron localizability indicator (ELI-D), ϒDσ(r), shows that the electronic structure of the central N–O bond is very sensitive to both electron correlation improvements (coupled-cluster single double (CCSD), CASSCF, density functional theory (DFT)) and bond length alteration. Depending on the method used, the N–O bond can be characterized as a “normal” N–O bond with a disynaptic V(N,O) basin (DFT); a protocovalent N–O bond with two monosynaptic, V(N) and V(O), basins (CCSD, CASSCF); or a new type, first discovered for FONO, characterized by a single monosynaptic, V(N) basin (CCSD, DFT). The total basin population oscillates between 0.46–0.96 e (CCSD) and 0.86–1.02 e (CASSCF). The X–O bond is described by the single disynaptic basin, V(X,O), with a basin population between 0.76 and 0.81 e (CCSD) or 0.77 and 0.85 e (CASSCF). Analysis of the localized electron detector distribution for the cis-Cl–O1–N=O2 shows a manifold in the Cl⋅⋅⋅O2 region, associated with decreased electron density.
Show PACS
31.15.E- Density-functional theory
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xr Self-consistent-field methods
33.15.Dj Interatomic distances and angles
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.bw Coupled-cluster theory

“Adiabatic-hindered-rotor” treatment of the parahydrogen-water complex

Tao Zeng, Hui Li, Robert J. Le Roy, and Pierre-Nicholas Roy

J. Chem. Phys. 135, 094304 (2011); http://dx.doi.org/10.1063/1.3626840 (15 pages) | Cited 1 time

Online Publication Date: 1 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Inspired by a recent successful adiabatic-hindered-rotor treatment for parahydrogen pH2 in CO2–H2 complexes [H. Li, P.-N. Roy, and R. J. Le Roy, J. Chem. Phys. 133, 104305 (2010); H. Li, R. J. Le Roy, P.-N. Roy, and A. R. W. McKellar, Phys. Rev. Lett. 105, 133401 (2010)], we apply the same approximation to the more challenging H2O–H2 system. This approximation reduces the dimension of the H2O–H2 potential from 5D to 3D and greatly enhances the computational efficiency. The global minimum of the original 5D potential is missing from the adiabatic 3D potential for reasons based on solution of the hindered-rotor Schrödinger equation of the pH2. Energies and wave functions of the discrete rovibrational levels of H2O–pH2 complexes obtained from the adiabatic 3D potential are in good agreement with the results from calculations with the full 5D potential. This comparison validates our approximation, although it is a relatively cruder treatment for pH2–H2O than it is for pH2–CO2. This adiabatic approximation makes large-scale simulations of H2O–pH2 systems possible via a pairwise additive interaction model in which pH2 is treated as a point-like particle. The poor performance of the diabatically spherical treatment of pH2 rotation excludes the possibility of approximating pH2 as a simple sphere in its interaction with H2O.
Show PACS
33.20.Vq Vibration-rotation analysis
31.50.-x Potential energy surfaces
31.15.B- Approximate calculations

The complex spectrum of a “simple” free radical: The math-math band system of the jet-cooled boron difluoride free radical

Jie Yang, Blaine Ellis, and Dennis J. Clouthier

J. Chem. Phys. 135, 094305 (2011); http://dx.doi.org/10.1063/1.3624528 (9 pages) | Cited 1 time

Online Publication Date: 2 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The near-ultraviolet band system of the jet-cooled boron difluoride free radical has been studied by a combination of laser-induced fluorescence and single vibronic level wavelength resolved emission spectroscopies. The radical was produced in a supersonic discharge jet using a precursor mixture of 1%–3% of BF3 or 10BF3 in high pressure argon. A large number of bands were found in the 340–286 nm region and assigned as transitions from the math2A1 ground state to the lower Renner-Teller component of the math2Π excited state, based on our previous ab initio potential energy surface predictions, matching the emission spectra Franck-Condon profiles of 11BF2 and 10BF2, and comparison of observed and calculated boron isotope effects. Several bands have been rotationally analyzed providing ground state structural parameters of r0′′ (BF) = 1.3102(9) Å and θ0′′ (FBF) = 119.7(6)°. The ground state totally symmetric vibrational energy levels of both boron isotopologues have also been measured and assigned up to energies of more than 8000 cm−1. Although BF2 might be considered to be a “simple” free radical, understanding the details of its electronic spectrum remains a major challenge for both theory and experiment.
Show PACS
33.20.Lg Ultraviolet spectra
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.50.Dq Fluorescence and phosphorescence spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Rovibrational bound states of neon trimer: Quantum dynamical calculation of all eigenstate energy levels and wavefunctions

Benhui Yang, Wenwu Chen, and Bill Poirier

J. Chem. Phys. 135, 094306 (2011); http://dx.doi.org/10.1063/1.3630922 (17 pages)

Online Publication Date: 2 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Exact quantum dynamics calculations of the eigenstate energy levels and wavefunctions for all bound rovibrational states of the Ne3 trimer (J = 0–18) have been performed using the ScalIT suite of parallel codes. These codes employ a combination of highly efficient methods, including phase-space optimized discrete variable representation, optimal separable basis, and preconditioned inexact spectral transform methods, together with an effective massive parallelization scheme. The Ne3 energy levels and wavefunctions were computed using a pair-wise Lennard-Jones potential. Jacobi coordinates were used for the calculations, but to identify just those states belonging to the totally symmetric irreducible representation of the G12 complete nuclear permutation-inversion group, wavefunctions were plotted in hyperspherical coordinates. “Horseshoe” states were observed above the isomerization barrier, but the horseshoe localization effect is weaker than in Ar3. The rigid rotor model is found to be applicable for only the ground and first excited vibrational states at low J; fitted rotational constant values are presented.
Show PACS
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.20.Cf Interatomic potentials and forces

Variational quantum mechanical and active database approaches to the rotational-vibrational spectroscopy of ketene, H2CCO

Csaba Fábri, Edit Mátyus, Tibor Furtenbacher, László Nemes, Béla Mihály, Tímea Zoltáni, and Attila G. Császár

J. Chem. Phys. 135, 094307 (2011); http://dx.doi.org/10.1063/1.3625404 (19 pages) | Cited 1 time

Online Publication Date: 2 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A variational quantum mechanical protocol is presented for the computation of rovibrational energy levels of semirigid molecules using discrete variable representation of the Eckart−Watson Hamiltonian, a complete, “exact” inclusion of the potential energy surface, and selection of a vibrational subspace. Molecular symmetry is exploited via a symmetry-adapted Lanczos algorithm. Besides symmetry labels, zeroth-order rigid-rotor and harmonic-oscillator quantum numbers are employed to characterize the computed rovibrational states. Using the computational molecular spectroscopy algorithm presented, a large number of rovibrational states, up to J = 50, of the ground electronic state of the parent isotopologue of ketene, H212C=12C=16O, were computed and characterized. Based on 12 references, altogether 3982 measured and assigned rovibrational transitions of H212C=12C=16O have been collected, from which 3194 were validated. These transitions form two spectroscopic networks (SN). The ortho and the para SNs contain 2489 and 705 validated transitions and 1251 and 471 validated energy levels, respectively. The computed energy levels are compared with energy levels obtained, up to J = 41, via an inversion protocol based on this collection of validated measured rovibrational transitions. The accurate inverted energy levels allow new assignments to be proposed. Some regularities and irregularities in the rovibrational spectrum of ketene are elucidated.
Show PACS
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.xt Variational techniques
31.15.ep Variational particle-number approach
33.20.Vq Vibration-rotation analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.50.Bc Potential energy surfaces for ground electronic states

Rotational analysis and deperturbation of the A 2Π → X 2Σ+ and B′ 2Σ+ → X 2Σ+ emission spectra of MgH

Alireza Shayesteh and Peter F. Bernath

J. Chem. Phys. 135, 094308 (2011); http://dx.doi.org/10.1063/1.3631341 (8 pages)

Online Publication Date: 6 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Deperturbation analysis of the A 2Π → X 2Σ+ and B′ 2Σ+ → X 2Σ+ emission spectra of 24MgH is reported. Spectroscopic data for the v = 0 to 3 levels of the A 2Π state and the v = 0 to 4 levels of the B′ 2Σ+ state were fitted together using a single Hamiltonian matrix that includes 2Π and 2Σ+ matrix elements, as well as off-diagonal elements coupling several vibrational levels of the two states. A Dunham-type fit was performed and the resulting Yl,0 and Yl,1 coefficients were used to generate Rydberg–Klein–Rees (RKR) potential curves for the A 2Π and the B′ 2Σ+ states. Vibrational overlap integrals were computed from the RKR potentials, and the off-diagonal matrix elements coupling the electronic wavefunctions (a+ and b) were determined. Zero point dissociation energies (D0) of the A 2Π and B′ 2Σ+ states of 24MgH were determined to be 12 957.5 ± 0.5 and 10 133.6 ± 0.5 cm−1, respectively. Using the Y0,1 coefficients, the equilibrium internuclear distances (re) of the A 2Π and B′ 2Σ+ states were determined to be 1.67827(1) Å and 2.59404(4) Å, respectively.
Show PACS
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
33.50.Dq Fluorescence and phosphorescence spectra
31.50.-x Potential energy surfaces
33.15.Fm Bond strengths, dissociation energies
33.15.Mt Rotation, vibration, and vibration-rotation constants

Collisional relaxation of O2(X3Σg−, υ = 1) and O2(a1Δg, υ = 1) by atmospherically relevant species

Dušan A. Pejaković, Zachary Campbell, Konstantinos S. Kalogerakis, Richard A. Copeland, and Tom G. Slanger

J. Chem. Phys. 135, 094309 (2011); http://dx.doi.org/10.1063/1.3624378 (18 pages)

Online Publication Date: 6 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Laboratory measurements are reported of the rate coefficient for collisional removal of O2(X3Σg−, υ = 1) by O(3P), and the rate coefficients for removal of O2(a1Δg, υ = 1) by O2, CO2, and O(3P). A two-laser method is employed, in which the pulsed output of the first laser at 285 nm photolyzes ozone to produce oxygen atoms and O2(a1Δg, υ = 1), and the output of the second laser detects O2(a1Δg, υ = 1) via resonance-enhanced multiphoton ionization. The kinetics of O2(X3Σg−, υ = 1) + O(3P) relaxation is inferred from the temporal evolution of O2(a1Δg, υ = 1), an approach enabled by the rapid collision-induced equilibration of the O2(X3Σg−, υ = 1) and O2(a1Δg, υ = 1) populations in the system. The measured O2(X3Σg−, υ = 1) + O(3P) rate coefficient is (2.9 ± 0.6) × 10−12 cm3 s−1 at 295 K and (3.4 ± 0.6) × 10−12 cm3 s−1 at 240 K. These values are consistent with the previously reported result of (3.2 ± 1.0) × 10−12 cm3 s−1, which was obtained at 315 K using a different experimental approach [K. S. Kalogerakis, R. A. Copeland, and T. G. Slanger, J. Chem. Phys. 123, 194303 (2005)]. For removal of O2(a1Δg, υ = 1) by O(3P), the upper limits for the rate coefficient are 4 × 10−13 cm3 s−1 at 295 K and 6 × 10−13 cm3 s−1 at 240 K. The rate coefficient for removal of O2(a1Δg, υ = 1) by O2 is (5.6 ± 0.6) × 10−11 cm3 s−1 at 295 K and (5.9 ± 0.5) × 10−11 cm3 s−1 at 240 K. The O2(a1Δg, υ = 1) + CO2 rate coefficient is (1.5 ± 0.2) × 10−14 cm3 s−1 at 295 K and (1.2 ± 0.1) × 10−14 cm3 s−1 at 240 K. The implications of the measured rate coefficients for modeling of atmospheric emissions are discussed.
Show PACS
82.20.Pm Rate constants, reaction cross sections, and activation energies
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

The spectroscopic characterization of the methoxy radical. III. Rotationally resolved math2A1–math2E electronic and math2E submillimeter wave spectra of partially deuterated CH2DO and CHD2O radicals

Dmitry G. Melnik, Jinjun Liu, Ming-Wei Chen, Terry A. Miller, and Robert F. Curl

J. Chem. Phys. 135, 094310 (2011); http://dx.doi.org/10.1063/1.3615724 (26 pages)

Online Publication Date: 7 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Rotationally resolved laser induced fluorescence and stimulated emission pumping math2A1−math2E spectra, along with pure rotational spectra in the 153–263 GHz region within the E3/2 component of the ground state in asymmetrically deuterated methoxy radicals CH2DO and CHD2O have been observed. The combined data set allows for the direct measurement with high precision of the energy separation between the E1/2 and E3/2 components of the ground state and the energy separation between the parity stacks in the E3/2 component of the ground state. The experimentally observed frequencies in both isotopologues are fit to an effective rotational Hamiltonian accounting for rotational and spin-rotational effects arising in a near-prolate asymmetric top molecule with dynamic Jahn-Teller distortion. Isotopic dependencies for the molecular parameters have been successfully implemented to aid the analysis of these very complex spectra. The analysis of the first and second order contributions to the effective values of molecular parameters has been extended to elucidate the physical significance of resulting molecular parameters. Comparisons of measured parameters, e.g., spin-orbit coupling, rotational and spin-rotation constants, are made among the 5 methoxy isotopologues for which data is now available. Comparisons of experimental results, including the derived geometric structure at both the C3v conical intersection and at the Jahn-Teller distorted minima, are made with quantum chemistry calculations.
Show PACS
33.20.Sn Rotational analysis
33.50.Dq Fluorescence and phosphorescence spectra
33.80.Be Level crossing and optical pumping
33.20.Bx Radio-frequency and microwave spectra
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.30.Gs Hyperfine interactions and isotope effects

An efficient route to thermal rate constants in reduced dimensional quantum scattering simulations: Applications to the abstraction of hydrogen from alkanes

H. F. von Horsten, S. T. Banks, and D. C. Clary

J. Chem. Phys. 135, 094311 (2011); http://dx.doi.org/10.1063/1.3625960 (14 pages)

Online Publication Date: 7 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present an efficient approach to the determination of two-dimensional potential energy surfaces for use in quantum reactive scattering simulations. Our method involves first determining the minimum energy path (MEP) for the reaction by means of an ab initio intrinsic reaction coordinate calculation. This one-dimensional potential is then corrected to take into account the zero point energies of the spectator modes. These are determined from Hessians in curvilinear coordinates after projecting out the modes to be explicitly treated in quantum scattering calculations. The final (1 + 1)-dimensional potential is constructed by harmonic expansion about each point along the MEP before transforming the whole surface to hyperspherical coordinates for use in the two-dimensional scattering simulations. This new method is applied to H-atom abstraction from methane, ethane and propane. For the latter, both reactive channels (producing i-C3H7 or n-C3H7) are investigated. For all reactions, electronic structure calculations are performed using an efficient, explicitly correlated, coupled cluster methodology (CCSD(T)-F12). Calculated thermal rate constants are compared to experimental and previous theoretical results.
Show PACS
31.15.ae Electronic structure and bonding characteristics
31.15.bw Coupled-cluster theory
31.50.-x Potential energy surfaces
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Conformer specific dissociation dynamics of iodocyclohexane studied by velocity map imaging

D. K. Zaouris, A. M. Wenge, D. Murdock, T. A. A. Oliver, G. Richmond, G. A. D. Ritchie, R. N. Dixon, and M. N. R. Ashfold

J. Chem. Phys. 135, 094312 (2011); http://dx.doi.org/10.1063/1.3628682 (8 pages) | Cited 1 time

Online Publication Date: 7 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The photodissociation dynamics of iodocyclohexane has been studied using velocity map imaging following excitation at many wavelengths within its A-band (230 ≤ λ ≤ 305 nm). This molecule exists in two conformations (axial and equatorial), and one aim of the present experiment was to explore the extent to which conformer-specific fragmentation dynamics could be distinguished. Ground (I) and spin-orbit excited (I*) state iodine atom products were monitored by 2 + 1 resonance enhanced multiphoton ionization, and total kinetic energy release (TKER) spectra and angular distributions derived from analysis of images recorded at all wavelengths studied. TKER spectra obtained at the longer excitation wavelengths show two distinct components, which can be attributed to the two conformers and the different ways in which these partition the excess energy upon C–I bond fission. Companion calculations based on a simple impulsive model suggest that dissociation of the equatorial (axial) conformer preferentially yields vibrationally (rotationally) excited cyclohexyl co-fragments. Both I and I* products are detected at the longest parent absorption wavelength (λ ∼ 305 nm), and both sets of products show recoil anisotropy parameters, β > 1, implying prompt dissociation following excitation via a transition whose dipole moment is aligned parallel to the C–I bond. The quantum yield for forming I* products, ΦI*, has been determined by time resolved infrared diode laser absorption methods to be 0.14 ± 0.02 (at λ = 248 nm) and 0.22 ± 0.05 (at λ = 266 nm). Electronic structure calculations indicate that the bulk of the A-band absorption is associated with transition to the 4A′ state, and that the (majority) I atom products arise via non-adiabatic transfer from the 4A′ potential energy surface (PES) via conical intersection(s) with one or more PESs correlating with ground state products.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation
FREE

Low-temperature tunneling and rotational dynamics of the ammonium cations in (NH4)2B12H12

Nina Verdal, Terrence J. Udovic, John J. Rush, Vitalie Stavila, Hui Wu, Wei Zhou, and Timothy Jenkins

J. Chem. Phys. 135, 094501 (2011); http://dx.doi.org/10.1063/1.3624495 (8 pages)

Online Publication Date: 1 September 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Low-temperature neutron scattering spectra of diammonium dodecahydro-closo-dodecaborate [(NH4)2B12H12] reveal two NH4+ rotational tunneling peaks (e.g., 18.5 μeV and 37 μeV at 4 K), consistent with the tetrahedral symmetry and environment of the cations. The tunneling peaks persist between 4 K and 40 K. An estimate was made for the tunnel splitting of the first NH4+ librational state from a fit of the observed ground-state tunnel splitting as a function of temperature. At temperatures of 50 K–70 K, classical neutron quasi-elastic scattering appears to dominate the spectra and is attributed to NH4+ cation jump reorientation about the four C3 axes defined by the N–H bonds. A reorientational activation energy of 8.1 ± 0.6 meV (0.79 ± 0.06 kJ/mol) is determined from the behavior of the quasi-elastic linewidths in this temperature regime. This activation energy is in accord with a change in NH4+ dynamical behavior above 70 K. A low-temperature inelastic neutron scattering feature at 7.8 meV is assigned to a NH4+ librational mode. At increased temperatures, this feature drops in intensity, having shifted entirely to higher energies by 200 K, suggesting the onset of quasi-free NH4+ rotation. This is consistent with neutron-diffraction-based model refinements, which derive very large thermal ellipsoids for the ammonium-ion hydrogen atoms at room temperature in the direction of reorientation.
Show PACS
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
33.70.Jg Line and band widths, shapes, and shifts
33.15.Fm Bond strengths, dissociation energies
33.15.Mt Rotation, vibration, and vibration-rotation constants
Page 1 of 2 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Breaking the carbon dimer: The challenges of multiple bond dissociation with full configuration interaction quantum Monte Carlo methods
  2. Perspective: The dawning of the age of graphene
  3. The submersion of sodium clusters in helium nanodroplets: Identification of the surface → interior transition
  4. Note: Accurate ab initio predictions of ionization energies of propargyl and allyl radicals: Revisited
  5. Conformational fluctuations of a protein–DNA complex and the structure and ordering of water around it
Go to AIP Home
Copyright © American Institute of Physics
close