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14 Jul 2010

Volume 133, Issue 2, Articles (02xxxx)

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J. Chem. Phys. 133, 024701 (2010); http://dx.doi.org/10.1063/1.3458691 (8 pages)

Víctor Antonio de la Peña O’Shea, Iberio de P. R. Moreira, Alberto Roldán, and Francesc Illas
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Communications: On the relation between the scalar and tensor exchange-correlation kernels of the time-dependent density-functional theory

V. U. Nazarov, G. Vignale, and Y.-C. Chang

J. Chem. Phys. 133, 021101 (2010); http://dx.doi.org/10.1063/1.3455711 (4 pages) | Cited 1 time

Online Publication Date: 13 July 2010

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The scalar fxc and tensor mathxc exchange-correlation (xc) kernels are key ingredients of the time-dependent density functional theory and the time-dependent current density functional theory, respectively. We derive a comparatively simple relation between these two kernels under the assumption that the dynamic xc can be considered “weak.” A calculation of the frequency-dependent dielectric function of silicon using this relation in conjunction with Vignale–Kohn mathxc demonstrates a potential of our method to account for the dynamic many-body effects within the rigorous scheme of time-dependent density functional theory. Our formula provides a bridge between the scalar fxc, which directly enters many applications, and the tensor mathxc which, due to its locality in space, is much easier to approximate.
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31.15.ee Time-dependent density functional theory
31.15.eg Exchange-correlation functionals (in current density functional theory)
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Communication: Energetics of reaction pathways for reactions of ethenol with the hydroxyl radical: The importance of internal hydrogen bonding at the transition state

Oksana Tishchenko, Sonia Ilieva, and Donald G. Truhlar

J. Chem. Phys. 133, 021102 (2010); http://dx.doi.org/10.1063/1.3455996 (4 pages) | Cited 5 times

Online Publication Date: 14 July 2010

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We find high multireference character for abstraction of H from the OH group of ethenol (also called vinyl alcohol); therefore we adopt a multireference approach to calculate barrier heights for the various possible reaction channels of OH+C2H3OH. The relative barrier heights of ten possible saddle points for reaction of OH with ethenol are predicted by multireference Møller–Plesset perturbation theory with active spaces based on correlated participating orbitals (CPOs) and CPO plus a correlated π orbital (CPO+π). Six barrier heights for abstracting H from a CH bond range from 3.1 to 7.7 kcal/mol, two barrier heights for abstracting H from an OH bond are both 6.0 kcal/mol, and two barrier heights for OH addition to the double bond are −1.8 and −2.8 kcal/mol. Thus we expect abstraction at high-temperature and addition at low temperature. The factor that determines which H is most favorable to abstract is an internal hydrogen bond that constitutes part of a six-membered ring at one of the abstraction saddle points; the hydrogen bond contributes about 3 kcal/mol stabilization.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Db Transition state theory and statistical theories of rate constants
33.15.Fm Bond strengths, dissociation energies
82.30.Nr Association, addition, insertion, cluster formation
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back to top Theoretical Methods and Algorithms

A numerical test of a high-penetrability approximation for the one-dimensional penetrable-square-well model

Riccardo Fantoni, Achille Giacometti, Alexandr Malijevský, and Andrés Santos

J. Chem. Phys. 133, 024101 (2010); http://dx.doi.org/10.1063/1.3455330 (14 pages) | Cited 4 times

Online Publication Date: 9 July 2010

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The one-dimensional penetrable-square-well fluid is studied using both analytical tools and specialized Monte Carlo simulations. The model consists of a penetrable core characterized by a finite repulsive energy combined with a short-range attractive well. This is a many-body one-dimensional problem, lacking an exact analytical solution, for which the usual van Hove theorem on the absence of phase transition does not apply. We determine a high-penetrability approximation complementing a similar low-penetrability approximation presented in previous work. This is shown to be equivalent to the usual Debye–Hückel theory for simple charged fluids for which the virial and energy routes are identical. The internal thermodynamic consistency with the compressibility route and the validity of the approximation in describing the radial distribution function is assessed by a comparison against numerical simulations. The Fisher–Widom line separating the oscillatory and monotonic large-distance behaviors of the radial distribution function is computed within the high-penetrability approximation and compared with the opposite regime, thus providing a strong indication of the location of the line in all possible regimes. The high-penetrability approximation predicts the existence of a critical point and a spinodal line, but this occurs outside the applicability domain of the theory. We investigate the possibility of a fluid-fluid transition by the Gibbs ensemble Monte Carlo techniques, not finding any evidence of such a transition. Additional analytical arguments are given to support this claim. Finally, we find a clustering transition when Ruelle’s stability criterion is not fulfilled. The consequences of these findings on the three-dimensional phase diagrams are also discussed.
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61.20.Ja Computer simulation of liquid structure
82.45.-h Electrochemistry and electrophoresis
64.70.Ja Liquid-liquid transitions
82.70.Dd Colloids

Performance of multireference and equation-of-motion coupled-cluster methods for potential energy surfaces of low-lying excited states: Symmetric and asymmetric dissociation of water

Xiangzhu Li and Josef Paldus

J. Chem. Phys. 133, 024102 (2010); http://dx.doi.org/10.1063/1.3451074 (13 pages) | Cited 3 times

Online Publication Date: 12 July 2010

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Multireference (MR), general-model-space (GMS), state-universal (SU) coupled-cluster (CC) method that considers singly (S) and doubly (D) excited cluster amplitudes relative to the reference configurations spanning the model space (GMS SU CCSD), as well as its externally corrected (ec) version (N,M)-CCSD that employs N-reference MR CISD as an external source of higher-than-pair cluster amplitudes in a M-reference GMS CCSD, are employed to investigate low-lying states of the water molecule. The emphasis is on a generation of several low lying states belonging to the same symmetry species. Cuts of the potential energy surface (PES) corresponding to the breaking of a single OH bond and leading to the OH+H fragments, as well as the simultaneous breaking of both bonds into the O+2H are considered. Relying on a simple ab initio model that enables a comparison with the exact full configuration interaction energies, the performance of the GMS-based methods is assessed in the whole relevant range of internuclear separations. It is shown that the ec (N,M)-CCSD version provides best results for both the singlet and the triplet states considered. The same cuts of the PES are then explored using a realistic aug-cc-pVTZ basis set. For triplets, the use of high-spin (MS = 1) references is to be preferred.
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31.15.bw Coupled-cluster theory
31.50.Df Potential energy surfaces for excited electronic states
31.15.ae Electronic structure and bonding characteristics
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
33.15.Fm Bond strengths, dissociation energies
31.15.vq Electron correlation calculations for polyatomic molecules

A tractable and accurate electronic structure method for static correlations: The perfect hextuples model

John A. Parkhill and Martin Head-Gordon

J. Chem. Phys. 133, 024103 (2010); http://dx.doi.org/10.1063/1.3456001 (10 pages) | Cited 5 times

Online Publication Date: 12 July 2010

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We present the next stage in a hierarchy of local approximations to complete active space self-consistent field (CASSCF) model in an active space of one active orbital per active electron based on the valence orbital-optimized coupled-cluster (VOO-CC) formalism. Following the perfect pairing (PP) model, which is exact for a single electron pair and extensive, and the perfect quadruples (PQ) model, which is exact for two pairs, we introduce the perfect hextuples (PH) model, which is exact for three pairs. PH is an approximation to the VOO-CC method truncated at hextuples containing all correlations between three electron pairs. While VOO-CCDTQ56 requires computational effort scaling with the 14th power of molecular size, PH requires only sixth power effort. Our implementation also introduces some techniques which reduce the scaling to fifth order and has been applied to active spaces roughly twice the size of the CASSCF limit without any symmetry. Because PH explicitly correlates up to six electrons at a time, it can faithfully model the static correlations of molecules with up to triple bonds in a size-consistent fashion and for organic reactions usually reproduces CASSCF with chemical accuracy. The convergence of the PP, PQ, and PH hierarchy is demonstrated on a variety of examples including symmetry breaking in benzene, the Cope rearrangement, the Bergman reaction, and the dissociation of fluorine.
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31.15.xr Self-consistent-field methods
31.15.bw Coupled-cluster theory
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Symmetry-adapted cluster and symmetry-adapted cluster-configuration interaction method in the polarizable continuum model: Theory of the solvent effect on the electronic excitation of molecules in solution

Roberto Cammi, Ryoichi Fukuda, Masahiro Ehara, and Hiroshi Nakatsuji

J. Chem. Phys. 133, 024104 (2010); http://dx.doi.org/10.1063/1.3456540 (24 pages) | Cited 7 times

Online Publication Date: 13 July 2010

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In this paper we present the theory and implementation of the symmetry-adapted cluster (SAC) and symmetry-adapted cluster-configuration interaction (SAC-CI) method, including the solvent effect, using the polarizable continuum model (PCM). The PCM and SAC/SAC-CI were consistently combined in terms of the energy functional formalism. The excitation energies were calculated by means of the state-specific approach, the advantage of which over the linear-response approach has been shown. The single-point energy calculation and its analytical energy derivatives are presented and implemented, where the free-energy and its derivatives are evaluated because of the presence of solute-solvent interactions. We have applied this method to s-trans-acrolein and metylenecyclopropene of their electronic excitation in solution. The molecular geometries in the ground and excited states were optimized in vacuum and in solution, and both the vertical and adiabatic excitations were studied. The PCM-SAC/SAC-CI reproduced the known trend of the solvent effect on the vertical excitation energies but the shift values were underestimated. The excited state geometry in planar and nonplanar conformations was investigated. The importance of using state-specific methods was shown for the solvent effect on the optimized geometry in the excited state. The mechanism of the solvent effect is discussed in terms of the Mulliken charges and electronic dipole moment.
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31.70.Dk Environmental and solvent effects

Electrostatic analysis of the interactions between charged particles of dielectric materials

Elena Bichoutskaia, Adrian L. Boatwright, Armik Khachatourian, and Anthony J. Stace

J. Chem. Phys. 133, 024105 (2010); http://dx.doi.org/10.1063/1.3457157 (10 pages) | Cited 3 times

Online Publication Date: 13 July 2010

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An understanding of the electrostatic interactions that exist between charged particles of dielectric materials has applications that span much of chemistry, physics, biology, and engineering. Areas of interest include cloud formation, ink-jet printing, and the stability of emulsions. A general solution to the problem of calculating electrostatic interactions between charged dielectric particles is presented. The solution converges very rapidly for low values of the dielectric constant and is stable up to the point where particles touch. Through applications to unspecified particles with a range of size and charge ratios, the model shows that there exist distinct regions of dielectric space where particles with the same sign of charge are strongly attracted to one another.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
82.70.Kj Emulsions and suspensions
77.22.Ch Permittivity (dielectric function)

A uniform source-and-sink scheme for calculating thermal conductivity by nonequilibrium molecular dynamics

Bing-Yang Cao (曹炳阳) and Yuan-Wei Li (李元伟)

J. Chem. Phys. 133, 024106 (2010); http://dx.doi.org/10.1063/1.3463699 (5 pages) | Cited 2 times

Online Publication Date: 14 July 2010

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A uniform source-and-sink (USS) scheme, which combines features of the reverse [ F. Müller-Plathe, J. Chem. Phys. 106, 6082 (1997) ] and improved relaxation [ B. Y. Cao, J. Chem. Phys. 129, 074106 (2008) ] methods, is developed to calculate the thermal conductivity by nonequilibrium molecular dynamics (NEMD). The uniform internal heat source and sink are realized by exchanging the velocity vectors of individual atoms in the right half and left half systems, and produce a periodically quadratic temperature profile throughout the system. The thermal conductivity can be easily extracted from the mean temperatures of the right and left half systems rather than by fitting the temperature profiles. In particular, this scheme greatly increases the relaxation of the exited localized phonon modes which often worsen the calculation accuracy and efficiency in most other NEMD methods. The calculation of the thermal conductivities of solid argon shows that the simple USS scheme gives accurate results with fast convergence.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Ab initio energy landscape of LiF clusters

K. Doll, J. C. Schön, and M. Jansen

J. Chem. Phys. 133, 024107 (2010); http://dx.doi.org/10.1063/1.3455708 (8 pages) | Cited 12 times

Online Publication Date: 14 July 2010

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A global search for possible LiF cluster structures is performed up to (LiF)8. The method is based on simulated annealing, where all the energies are evaluated on the ab initio level. In addition, the threshold algorithm is employed to determine the energy barriers for the transitions among these structures, for the cluster (LiF)4, again on the ab initio level, and the corresponding tree graph is obtained.
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36.40.Cg Electronic and magnetic properties of clusters
31.15.ae Electronic structure and bonding characteristics
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Proton formation dynamics in the REMPI[2+n] process via the F 1Δ2 and f 3Δ2 Rydberg states of HCl investigated by three-dimensional velocity mapping

S. Kauczok, C. Maul, A. I. Chichinin, and K.-H. Gericke

J. Chem. Phys. 133, 024301 (2010); http://dx.doi.org/10.1063/1.3427541 (10 pages) | Cited 2 times

Online Publication Date: 9 July 2010

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HCl in the bulk gas phase at a pressure of 10−5 mbar has been excited via selected Q-lines of the two-photon transition band systems F 1Δ2←X 1Σ+(1,0) [Q(8)], V 1Σ+←X 1Σ+(14,0) [Q(8), Q(7)] and f 3Δ2←X 1Σ+(0,0) [Q(2–6)]. Concerning the V←X excitation, subsequent photon absorption is known to yield HCl+, H(n = 2)+Cl, H++Cl− and H+Cl(4s,4p,3d). Vibrationally excited HCl+ (v+ ≥ 5) can be photodissociated to H++Cl, and excited atoms can be easily photoionized by absorption of a fourth photon, respectively. Using three-dimensional velocity map imaging, the spatial proton velocity distributions resulting from these processes for these particular transitions were studied for the first time. Kvaran et al. [J. Chem. Phys. 131, 044324 (2009) ; J. Chem. Phys. 129, 164313 (2008)] recently reported a substantial increase in the formation of chlorine and hydrogen ions in single rovibrational transitions of the F 1Δ2 and f 3Δ2 band systems using mass resolved resonance enhanced multiphoton ionization spectroscopy and explained this by the vicinity of single rovibrational levels of the V 1Σ+ state for which photorupture is the main feature. Thus, the known dissociation dynamics of the V 1Σ+ state should also leave their fingerprint in the spatial proton velocity distribution emerging from the photodissociation of those states. Accordingly, we found a strong increase in the H+ ion signal for the Q(5) line of the f 3Δ2←X 1Σ+(0,0) transition, the extra signal resulting from dissociation into H(n = 2)+Cl(2P1/2) and the ion pair. No increase for the HCl+(v+ ≥ 5) photodissociation channel or dissociation into H(n = 2)+Cl(2P3/2) has been observed. Furthermore, H+ distributions from the Q transitions of the f 3Δ2←X 1Σ+(0,0) band system were found to show the two features previously ascribed to the “gateway” state [4Π⋯4s]3Π(0), i.e., autoionization into HCl+(5 ≤ v+ ≤ 8) and nonadiabatic dissociation into H(n = 2)+Cl(2P3/2). The F 1Δ2←X 1Σ+(1,0) band system only showed significant proton formation for the Q(8) line. The speed distribution is the same as for the Q(8,7) lines of the V 1Σ+←X 1Σ+(14,0) transition while the excitation history is conserved in the angular distribution confirming the resonance interpretation.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Vq Vibration-rotation analysis
33.20.Tp Vibrational analysis
33.15.Ta Mass spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Measuring the conformational properties of 1,2,3,6,7,8-hexahydropyrene and its van der Waals complexes

Philip J. Morgan, Joseph R. Roscioli, Adam J. Fleisher, and David W. Pratt

J. Chem. Phys. 133, 024302 (2010); http://dx.doi.org/10.1063/1.3455341 (7 pages)

Online Publication Date: 9 July 2010

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Rotationally resolved fluorescence excitation spectra of the S1←S0 origin band transitions of two conformers of 1,2,3,6,7,8-hexahydropyrene (HHP) have been recorded in the gas phase. The band at 30 648.0 cm−1 has been assigned as the origin band of the chair conformer and the band at 30 658.8 cm−1 has been assigned as the origin band of the boat conformer on the basis of differences in their rotational constants. In addition, rotationally resolved fluorescence excitation spectra of single Ar and H2O van der Waals complexes of chair-HHP have been observed. Analyses of these results indicate that the weakly attached argon atom (water molecule) is located on top of the plane of the bare molecule at ∼ 3.4 Å ( ∼ 4.1 Å) from its center of mass in the S0 electronic state. No complexes of boat-HHP were detected.
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33.15.Mt Rotation, vibration, and vibration-rotation constants

Rotationally resolved electronic spectroscopy of 5-methoxyindole

Christian Brand, Olivia Oeltermann, David Pratt, Rainer Weinkauf, W. Leo Meerts, Wim van der Zande, Karl Kleinermanns, and Michael Schmitt

J. Chem. Phys. 133, 024303 (2010); http://dx.doi.org/10.1063/1.3459128 (11 pages) | Cited 5 times

Online Publication Date: 9 July 2010

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Rotationally resolved electronic spectra of the vibrationless origin and of eight vibronic bands of 5-methoxyindole (5MOI) have been measured and analyzed using an evolutionary strategy approach. The experimental results are compared to the results of ab initio calculations. All vibronic bands can be explained by absorption of a single conformer, which unambiguously has been shown to be the anti-conformer from its rotational constants and excitation energy. For both anti- and syn-conformers, a 1La/1Lb gap larger than 4000 cm−1 is calculated, making the vibronic coupling between both states very small, thereby explaining why the spectrum of 5MOI is very different from that of the parent molecule, indole.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

Higher energy electronic transitions of HC2n+1H+ (n = 2–7) and HC2n+1H (n = 4–7) in neon matrices

Jan Fulara, Adam Nagy, Iryna Garkusha, and John P. Maier

J. Chem. Phys. 133, 024304 (2010); http://dx.doi.org/10.1063/1.3455208 (9 pages) | Cited 6 times

Online Publication Date: 12 July 2010

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Electronic absorption spectra of linear HC2n+1H+ (n = 2–7) were recorded in 6 K neon matrices following their mass-selective deposition. Four new electronic band systems are identified; the strongest math 2Πg/u←math 2Πu/g lies in the UV and the second most intense math 2Πg/u←math 2Πu/g is located in the visible range. The known math 2Πg/u←math 2Πu/g absorption is an order of magnitude weaker than math 2Πg/u←math 2Πu/g. Transitions to the math and math states are also discussed. The wavelengths of the HC2n+1H+ (n = 2–7) electronic systems obey a linear relation as a function of the size of the cations, similar to other carbon chains. The math 3Σu−←math 3Σg− transition in the UV of neutral HC2n+1H (n = 4–7) has also been identified upon photobleaching of the cations trapped in the matrices.
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33.20.Kf Visible spectra
33.20.Lg Ultraviolet spectra
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

CO2 reduction by group 6 transition metal suboxide cluster anions

Ekram Hossain, David W. Rothgeb, and Caroline Chick Jarrold

J. Chem. Phys. 133, 024305 (2010); http://dx.doi.org/10.1063/1.3455220 (10 pages) | Cited 4 times

Online Publication Date: 12 July 2010

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Reactions between small group 6 transition metal suboxide clusters, MxOy− (M = 98Mo or 186W; x = 1−4; y ≤ 3x) and both CO2 and CO were studied in gas phase using mass spectrometric analysis of high-pressure, fast flow reaction products. Both Mo2Oy− and W2Oy− show evidence of sequential oxidation by CO2 of the form, M2Oy−+CO2→M2Oy+1−+CO for the more reduced species. Similar evidence is observed for the trimetallic clusters, although Mo3O6− appears uniquely unreactive. Lower mass resolution in the M4Oy− range precludes definitive product mass assignments, but intensity patterns suggest the continued trend of sequential oxidation of the more reduced end of the M4Oy− oxide series. Based on thermodynamic arguments, cluster oxidation by CO2 is possible if D0(OMoxOy−)>5.45 eV. Although simple bond energy analysis suggests that tungsten oxides may be more reactive toward CO2 compared to molybdenum oxides, this is not born out experimentally, suggesting that the activation barrier for the reduction of CO2 by tungsten suboxide clusters is very high compared to analogous molybdenum suboxide clusters. In reactions with CO, suboxides of both metal-based oxides show CO addition, with the product distribution being more diverse for MoxOy− than for WxOy−. No evidence of cluster reduction by CO is observed.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Pm Rate constants, reaction cross sections, and activation energies
36.40.Jn Reactivity of clusters
82.33.Fg Reactions in clusters

A new accurate and full dimensional potential energy surface of H5+ based on a triatomics-in-molecules analytic functional form

A. Aguado, P. Barragán, R. Prosmiti, G. Delgado-Barrio, P. Villarreal, and O. Roncero

J. Chem. Phys. 133, 024306 (2010); http://dx.doi.org/10.1063/1.3454658 (15 pages) | Cited 6 times

Online Publication Date: 14 July 2010

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In this work a reliable full nine-dimensional potential energy surface for studying the dynamics of H5+ is constructed, which is completely symmetric under any permutation of the nuclei. For this purpose, we develop a triatoms-in-molecules method as an extension of the more common diatoms-in-molecules one, which allows a very accurate description of the asymptotic regions by including correctly the charge-induced dipole and quadrupole interactions. Moreover, this treatment provides a semiquantitative description of all the topological features of the global potential compared with coupled cluster results. In particular, the hop of the proton between two H2 fragments produces a double well in the potential. This resonant structure involving the five atoms produces a stabilization, lowering the barrier, and the triatoms-in-molecules yields to a barrier significantly higher than the ab initio results. Therefore, to improve the triatomics-in-molecules potential surface, two five-body terms are added, which are fitted to more than 110 000 coupled-cluster ab initio points. The global potential energy surface thus obtained in this work has an overall root mean square error of 0.079 kcal/mol for energies below 27 kcal/mol above the global well. The features of the potential are described and compared with previous available surfaces.
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31.50.Df Potential energy surfaces for excited electronic states
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.bw Coupled-cluster theory
31.15.A- Ab initio calculations

Ab initio study of the 1 2Δ-math 2Π electronic transition of C2As

Stanka Jerosimić, Ljiljana Stojanović, and Miljenko Perić

J. Chem. Phys. 133, 024307 (2010); http://dx.doi.org/10.1063/1.3456538 (10 pages) | Cited 1 time

Online Publication Date: 14 July 2010

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We report the results of ab initio calculations on the 1 2Δ-math 2Π spectral system of C2As. The present study is closely related to the recent comprehensive experimental and theoretical work by Wei et al. [J. Chem. Phys. 129, 134307 (2008)] . By means of the state-average complete active space self-consistent field and multireference configuration interaction approach, we computed the vertical excitation energies to the low-lying doublet electronic species, potential surfaces and spin-orbit constants for the math 2Π and 1 2Δ states, as well as the components of the electric dipole moment for the transition between these two species. Using these data, we calculated the vibronic energy levels, the spin-orbit structure of the spectrum, and the vibronic transition moments of the math 2Π-1 2Δ system. The results of the present study for the X 2Π state agree with those derived from experimental findings by Wei et al., they elucidate the vibronic and spin-orbit structure in the 1 2Δ species, and offer predictions for experimental searches of heretofore unobserved electronic states.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.50.-x Potential energy surfaces
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.15.xr Self-consistent-field methods

Ultraviolet photochemistry of buta-1,3- and buta-1,2-dienes: Laser spectroscopic absolute hydrogen atom quantum yield and translational energy distribution measurements

A. Hanf, H.-R. Volpp, P. Sharma, J. P. Mittal, and R. K. Vatsa

J. Chem. Phys. 133, 024308 (2010); http://dx.doi.org/10.1063/1.3462951 (8 pages)

Online Publication Date: 14 July 2010

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Using pulsed H-atom Lyman-α laser-induced fluorescence spectroscopy along with a photolytic calibration approach, absolute H-atom product quantum yields of ϕH-b13d = (0.32±0.04) and ϕH-b12d = (0.36±0.04) were measured under collision-free conditions for the 193 nm gas-phase laser flash photolysis of buta-1,3- and buta-1,2-diene at room temperature, which demonstrate that nascent H-atom formation is of comparable importance for both parent molecules. Comparison of the available energy fraction, fT-b13d = (0.22±0.03) and fT-b12d = (0.13±0.01), released as H+C4H5 product translational energy with results of impulsive and statistical energy partitioning modeling calculations indicates that for both, buta-1,3- and buta-1,2-diene, H-atom formation is preceded by internal conversion to the respective electronic ground state (S0) potential energy surfaces. In addition, values of σb-1,3-d-Lα = (3.5±0.2)×10−17 cm2 and σb-1,2-d-Lα = (4.4±0.2)×10−17 cm2 for the previously unknown Lyman-α (121.6 nm) radiation photoabsorption cross sections of buta-1,3- and buta-1,2-diene in the gas-phase were determined.
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82.50.Hp Processes caused by visible and UV light
82.20.Kh Potential energy surfaces for chemical reactions
33.80.Gj Diffuse spectra; predissociation, photodissociation
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Non-Condon effect on charge transport in dithiophene-tetrathiafulvalene crystal

WeiWei Zhang, WanZhen Liang, and Yi Zhao

J. Chem. Phys. 133, 024501 (2010); http://dx.doi.org/10.1063/1.3456545 (11 pages) | Cited 4 times

Online Publication Date: 8 July 2010

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Combining first-principles calculations and non-Condon charge transfer rates proposed by us recently [ Y. Zhao and W. Z. Liang, J. Chem. Phys. 130, 034111 (2009) ], we investigated non-Condon effect on charge carrier mobility of organic semiconductor dithiophene-tetrathiafulvalene (DT-TTF) crystal. The first-principles results reveal that only several high-frequency intramolecular vibrational modes dominate the reorganization energy, and the nuclear-coordinate dependence of electronic coupling prefers to perform an exponential or Gaussian property for most intermolecular modes rather than a linear one as assumed in conventional models. Furthermore, the electronic coupling of an isolated DT-TTF dimer is indeed affected by the surrounding molecules. The predicted non-Condon mobilities with use of the obtained structure parameters are always greater than those from Condon approximation, and the non-Condon dynamic disorder is not important for DT-TTF, which is also confirmed by molecular dynamics simulation. More interestingly, the bandlike property can be predicted under the hopping mechanism when the nuclear tunneling is incorporated.
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71.15.-m Methods of electronic structure calculations
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Collective excitations in supercritical fluids: Analytical and molecular dynamics study of “positive” and “negative” dispersion

Taras Bryk, Ihor Mryglod, Tullio Scopigno, Giancarlo Ruocco, Federico Gorelli, and Mario Santoro

J. Chem. Phys. 133, 024502 (2010); http://dx.doi.org/10.1063/1.3442412 (8 pages) | Cited 4 times

Online Publication Date: 8 July 2010

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The approach of generalized collective modes is applied to the study of dispersion curves of collective excitations along isothermal lines of supercritical pure Lennard-Jones fluid. An effect of structural relaxation and other nonhydrodynamic relaxation processes on the dispersion law is discussed. A simple analytical expression for the dispersion law in the long-wavelength region of acoustic excitations is obtained within a three-variable viscoelastic model of generalized hydrodynamics. It is shown that the deviation from the linear dependence in the long-wavelength region can be either “positive” or “negative” depending on the ratio between the high-frequency (elastic) and isothermal speed of sound. An effect of thermal fluctuations on positive and negative dispersion is estimated from the analytical solution of a five-variable thermoviscoelastic model that generalizes the results of the viscoelastic treatment. Numerical results are reported for a Lennard-Jones supercritical fluid along two isothermal lines T∗ = 1.71,4.78 with different densities and discussed along the theoretical expressions derived.
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61.20.Ja Computer simulation of liquid structure
61.25.-f Studies of specific liquid structures
62.60.+v Acoustical properties of liquids
61.20.-p Structure of liquids

Low-frequency Raman spectra and fragility of imidazolium ionic liquids

Mauro C. C. Ribeiro

J. Chem. Phys. 133, 024503 (2010); http://dx.doi.org/10.1063/1.3462962 (6 pages) | Cited 3 times

Online Publication Date: 9 July 2010

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Raman spectra within the 5–200 cm−1 range have been recorded as a function of temperature for different ionic liquids based on imidazolium cations. A correlation has been found between fragility and the temperature dependence of the strength of fast relaxational motions. Understanding quasielastic scattering as the relaxational contribution to ionic mean-squared displacement elucidates some effects on ionic liquids’ fragility resulting from modifications in the chemical structure.
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78.30.C- Liquids
61.66.Hq Organic compounds
25.70.-z Low and intermediate energy heavy-ion reactions

Enhancement of the water proton relaxivity by trapping Gd3+ complexes in nanovesicles

Pascal H. Fries and Elie Belorizky

J. Chem. Phys. 133, 024504 (2010); http://dx.doi.org/10.1063/1.3456987 (6 pages) | Cited 4 times

Online Publication Date: 12 July 2010

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We present a theoretical model for calculating the relaxivity of the water protons due to Gd3+ complexes trapped inside nanovesicles, which are permeable to water. The formalism is applied to the characterization of apoferritin systems [ S. Aime et al., Angew. Chem., Int. Ed. 41, 1017 (2002) ; O. Vasalatiy et al., Contrast Media Mol. Imaging 1, 10 (2006) ]. The very high relaxivity due to these systems is attributed to an increase of the local viscosity of the aqueous solution inside the vesicles and to an outer-sphere mechanism which largely dominates the inner-sphere contribution. We discuss how to tailor the dynamic parameters of the trapped complexes in order to optimize the relaxivity. More generally, the potential of relaxivity studies for investigating the local dynamics and residence time of exchangeable molecules in nanovesicles is pointed out.
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61.20.Ja Computer simulation of liquid structure
66.20.-d Viscosity of liquids; diffusive momentum transport

Mode-dependent dispersion in Raman line shapes: Observation and implications from ultrafast Raman loss spectroscopy

S. Umapathy, B. Mallick, and A. Lakshmanna

J. Chem. Phys. 133, 024505 (2010); http://dx.doi.org/10.1063/1.3464332 (6 pages) | Cited 4 times

Online Publication Date: 13 July 2010

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Ultrafast Raman loss spectroscopy (URLS) enables one to obtain the vibrational structural information of molecular systems including fluorescent materials. URLS, a nonlinear process analog to stimulated Raman gain, involves a narrow bandwidth picosecond Raman pump pulse and a femtosecond broadband white light continuum. Under nonresonant condition, the Raman response appears as a negative (loss) signal, whereas, on resonance with the electronic transition the line shape changes from a negative to a positive through a dispersive form. The intensities observed and thus, the Franck–Condon activity (coordinate dependent), are sensitive to the wavelength of the white light corresponding to a particular Raman frequency with respect to the Raman pump pulse wavelength, i.e., there is a mode-dependent response in URLS.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.50.Dq Fluorescence and phosphorescence spectra
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
33.70.Jg Line and band widths, shapes, and shifts
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Structural transitions and dipole moment of water clusters (H2O)n = 4–100

Julián Gelman-Constantin, Marcelo A. Carignano, Igal Szleifer, Ernesto J. Marceca, and Horacio R. Corti

J. Chem. Phys. 133, 024506 (2010); http://dx.doi.org/10.1063/1.3455716 (8 pages) | Cited 2 times

Online Publication Date: 14 July 2010

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The properties of water clusters (H2O)n over a broad range of sizes (n = 4–100) were studied by microcanonical parallel tempering Monte Carlo and replica exchange molecular dynamics simulations at temperatures between 20 and 300 K, with special emphasis in the understanding of relation between the structural transitions and dipole behavior. The effect of the water interaction potential was analyzed using six nonpolarizable models, but more extensive calculations were performed using the TIP4P-ice water model. We find that, in general, the dipole moment of the cluster increases significantly as the cluster melts, suggesting that it could be used to discriminate between the solidlike and liquidlike phases. The effect of a moderate electric field on the cluster heat capacity and total dipole moment was found to be negligible.
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36.40.Mr Spectroscopy and geometrical structure of clusters
02.70.Uu Applications of Monte Carlo methods
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.xv Molecular dynamics and other numerical methods

Toward the origin of exciton electronic structure in phycobiliproteins

Jordan M. Womick, Stephen A. Miller, and Andrew M. Moran

J. Chem. Phys. 133, 024507 (2010); http://dx.doi.org/10.1063/1.3457378 (10 pages) | Cited 3 times

Online Publication Date: 14 July 2010

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Femtosecond laser spectroscopies are used to examine the electronic structures of two proteins found in the phycobilisome antenna of cyanobacteria, allophycocyanin (APC) and C-phycocyanin (CPC). The wave function composition involving the pairs of phycocyanobilin pigments (i.e., dimers) found in both proteins is the primary focus of this investigation. Despite their similar geometries, earlier experimental studies conducted in our laboratory and elsewhere observe clear signatures of exciton electronic structure in APC but not CPC. This issue is further investigated here using new experiments. Transient grating (TG) experiments employing broadband quasicontinuum probe pulses find a redshift in the signal spectrum of APC, which is almost twice that of CPC. Dynamics in the TG signal spectra suggest that the sub-100 fs dynamics in APC and CPC are respectively dominated by internal conversion and nuclear relaxation. A specialized technique, intraband electronic coherence spectroscopy (IECS), photoexcites electronic and nuclear coherences with nearly full suppression of signals corresponding to electronic populations. The main conclusion drawn by IECS is that dephasing of intraband electronic coherences in APC occurs in less than 25 fs. This result rules out correlated pigment fluctuations as the mechanism enabling exciton formation in APC and leads us to propose that the large Franck–Condon factors of APC promote wave function delocalization in the vibronic basis. For illustration, we compute the Hamiltonian matrix elements involving the electronic origin of the α84 pigment and the first excited vibronic level of the β84 pigment associated with a hydrogen out-of-plane wagging mode at 800 cm−1. For this pair of vibronic states, the −51 cm−1 coupling is larger than the 40 cm−1 energy gap, thereby making wave function delocalization a feasible prospect. By contrast, CPC possesses no pair of vibronic levels for which the intermolecular coupling is larger than the energy gap between vibronic states. This study of APC and CPC may be important for understanding the photophysics of other phycobiliproteins, which generally possess large vibronic couplings.
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87.15.-v Biomolecules: structure and physical properties
33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)
back to top Surfaces, Interfaces, and Materials

Electronic and magnetic structure of bulk cobalt: The α, β, and ε-phases from density functional theory calculations

Víctor Antonio de la Peña O’Shea, Iberio de P. R. Moreira, Alberto Roldán, and Francesc Illas

J. Chem. Phys. 133, 024701 (2010); http://dx.doi.org/10.1063/1.3458691 (8 pages) | Cited 1 time

Online Publication Date: 8 July 2010

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The geometric, electronic and magnetic properties of the three metallic cobalt phases: hcp(α), fcc(β), and epsilon(ε) have been theoretically studied using periodic density functional calculations with generalized gradient approximation (GGA) and plane wave basis set. These results have been compared with those obtained with GGA+U approach which have shown a noticeable improvement with regard to experimental data. For instance, the cohesive energy values predicted by GGA are overestimated by ∼ 25%, whereas GGA+U underestimate them by 14%–17%. On the other hand, magnetic moment values are underestimated in GGA while are overestimated for GGA+U approach by almost the same amount. Besides, the introduction of U parameter gives rise to an electronic redistribution in the d-band structure, which leads to variations in the magnetic properties. Moreover, a higher attention has been paid in the study of the electronic and magnetic properties of the ε-phase that has not described previously. These studies show that this phase posses special properties that could lead to an unusual behavior in magnetic or catalytic applications.
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71.20.Be Transition metals and alloys
75.30.Cr Saturation moments and magnetic susceptibilities
71.15.Nc Total energy and cohesive energy calculations
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
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