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7 Jun 2009

Volume 130, Issue 21, Articles (21xxxx)

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J. Chem. Phys. 130, 214501 (2009); http://dx.doi.org/10.1063/1.3139064 (14 pages)

Giuseppe Pileio and Malcolm H. Levitt
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Announcement: Free access to Communications published in The Journal of Chemical Physics

Mark M. Cassar

J. Chem. Phys. 130, 210201 (2009); http://dx.doi.org/10.1063/1.3153522 (1 page)

Online Publication Date: 2 June 2009

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01.10.Cr Announcements, news, and awards
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Adiabatic ionization potential of acetic acid and torsional dynamics of its cation

Philipp Zielke, Piotr W. Forysinski, David Luckhaus, and Ruth Signorell

J. Chem. Phys. 130, 211101 (2009); http://dx.doi.org/10.1063/1.3149802 (3 pages) | Cited 4 times

Online Publication Date: 1 June 2009

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Pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy and supersonic cooling are used to investigate the CH3 torsional dynamics of the acetic acid cation and to determine an accurate value for the first adiabatic ionization potential of acetic acid (IP = 85 912±5 cm−1), which has been the subject of debates for more than 40 yr. A doubling of the torsional barrier upon ionization is due to a significant shortening of the C–C bond and reduces the tunneling efficiency by an order of magnitude.
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33.60.+q Photoelectron spectra
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
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Zeroth order regular approximation approach to parity violating nuclear magnetic resonance shielding tensors

Sophie Nahrwold and Robert Berger

J. Chem. Phys. 130, 214101 (2009); http://dx.doi.org/10.1063/1.3103643 (14 pages) | Cited 3 times

Online Publication Date: 1 June 2009

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In this paper, a quasirelativistic two-component zeroth order regular approximation (ZORA) density functional theory (DFT) approach to the calculation of parity violating (PV) resonance frequency differences between the nuclear magnetic resonance (NMR) spectra of enantiomers is presented and the systematics of PV NMR shielding constants in C2-symmetric dihydrogen dichalcogenides (H2X2 with X = 17O, 33S, 77Se, 125Te, 209Po) are investigated. The typical sin(2α)-like dependence of the PV NMR frequency splittings on the dihedral angle α is observed for the entire series. As for the scaling behavior of the effect with the nuclear charge Z of X, the previously reported Z2.5±0.5 scaling in the nonrelativistic limit is reproduced and a scaling of approximately Z3 for the paramagnetic and Z5 for the spin-orbit coupling contribution to the frequency splitting is observed in the relativistic framework. The paramagnetic and spin-orbit coupling contributions are typically of opposite sign for the molecular structures studied herein and the maximum scaling of the total ZORA frequency splitting (i.e., the sum of the two contributions) is Z3.9 for H2Po2. Thus, an earlier claim for a spin-orbit coupling contribution scaling with up to Z7 for H2Po2 and the erratic dihedral angle dependence obtained for this compound within a four-component Dirac–Hartree–Fock–Coulomb study is not confirmed at the DFT level. The maximum NMR frequency splitting reported here is of the order of 10 mHz for certain clamped conformations of H2Po2 inside a static magnetic field with magnetic flux density of 11.7 T. Frequency splittings of this size have been estimated to be detectable with present day NMR spectrometers. Thus, a NMR route toward molecular PV appears promising once suitable compounds have been identified.
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33.25.+k Nuclear resonance and relaxation
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.30.jg QED corrections to parity nonconserving transition amplitudes and CP violations
31.15.E- Density-functional theory

Coarse graining and scaling in dissipative particle dynamics

Rudolf M. Füchslin, Harold Fellermann, Anders Eriksson, and Hans-Joachim Ziock

J. Chem. Phys. 130, 214102 (2009); http://dx.doi.org/10.1063/1.3143976 (8 pages) | Cited 6 times

Online Publication Date: 2 June 2009

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Dissipative particle dynamics (DPD) is now a well-established method for simulating soft matter systems. However, its applicability was recently questioned because some investigations showed an upper coarse-graining limit that would prevent the applicability of the method to the whole mesoscopic range. This article aims to re-establish DPD as a truly mesoscopic method by analyzing the problems reported by other authors and by presenting a scaling scheme that allows one to apply DPD simulations directly to any desired length scale.
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73.23.-b Electronic transport in mesoscopic systems
64.60.ae Renormalization-group theory

Effects of nonmagnetic impurities on the spin transport property of a graphene nanoribbon device

Joonho Park, Heok Yang, K.-S. Park, and Eok-Kyun Lee

J. Chem. Phys. 130, 214103 (2009); http://dx.doi.org/10.1063/1.3138776 (7 pages) | Cited 4 times

Online Publication Date: 3 June 2009

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Using a nonequilibrium density functional calculation, we investigated the electronic transport properties and fundamental mechanism of spin polarization as a function of the location of impurities from the center to an edge of a graphene nanoribbon device (GND) with zigzag edges. A center-located impurity enables both edges to be enhanced with respect to their spin transports whereas an edge-located impurity results in only the opposite edge channel being dominant. In the case of a center-located impurity, the ferromagnetic ground state induces new spin states near the Fermi level responsible for the spin-polarized current in the GND. We argue that the spin-polarized current can flow through the edge states induced by a nonmagnetic impurity around the Fermi level, especially on a GND with a center-located impurity.
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85.35.-p Nanoelectronic devices
72.25.Mk Spin transport through interfaces

A branch-point approximant for the equation of state of hard spheres

Andrés Santos and Mariano López de Haro

J. Chem. Phys. 130, 214104 (2009); http://dx.doi.org/10.1063/1.3147723 (5 pages) | Cited 3 times

Online Publication Date: 4 June 2009

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Using the first seven known virial coefficients and forcing it to possess two branch-point singularities, a new equation of state for the hard-sphere fluid is proposed. This equation of state predicts accurate values of the higher virial coefficients, a radius of convergence smaller than the close-packing value, and it is as accurate as the rescaled virial expansion and better than the Padé [3/3] equations of state. Consequences regarding the convergence properties of the virial series and the use of similar equations of state for hard-core fluids in d dimensions are also pointed out.
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61.20.Gy Theory and models of liquid structure
64.10.+h General theory of equations of state and phase equilibria

Multidimensional generalized-ensemble algorithms for complex systems

Ayori Mitsutake and Yuko Okamoto

J. Chem. Phys. 130, 214105 (2009); http://dx.doi.org/10.1063/1.3127783 (14 pages) | Cited 5 times

Online Publication Date: 4 June 2009

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We give general formulations of the multidimensional multicanonical algorithm, simulated tempering, and replica-exchange method. We generalize the original potential energy function E0 by adding any physical quantity V of interest as a new energy term. These multidimensional generalized-ensemble algorithms then perform a random walk not only in E0 space but also in V space. Among the three algorithms, the replica-exchange method is the easiest to perform because the weight factor is just a product of regular Boltzmann-like factors, while the weight factors for the multicanonical algorithm and simulated tempering are not a priori known. We give a simple procedure for obtaining the weight factors for these two latter algorithms, which uses a short replica-exchange simulation and the multiple-histogram reweighting techniques. As an example of applications of these algorithms, we have performed a two-dimensional replica-exchange simulation and a two-dimensional simulated-tempering simulation using an α-helical peptide system. From these simulations, we study the helix-coil transitions of the peptide in gas phase and in aqueous solution.
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31.15.X- Alternative approaches
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Hybrid particle-field molecular dynamics simulations for dense polymer systems

Giuseppe Milano and Toshihiro Kawakatsu

J. Chem. Phys. 130, 214106 (2009); http://dx.doi.org/10.1063/1.3142103 (8 pages) | Cited 4 times

Online Publication Date: 4 June 2009

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We propose a theoretical scheme for a hybrid simulation technique where self-consistent field theory and molecular dynamics simulation are combined (MD-SCF). We describe the detail of the main implementation issues on the evaluation of a smooth three-dimensional spatial density distribution and its special gradient based on the positions of particles. The treatments of our multiscale model system on an atomic scale or on a specific coarse-grained scale are carefully discussed. We perform a series of test simulations on this hybrid model system and compare the structural correlations on the atomic scale with those of classical MD simulations. The results are very encouraging and open a way to an efficient strategy that possess the main advantages common to the SCF and the atomistic approaches, while avoiding the disadvantages of each of the treatments.
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61.41.+e Polymers, elastomers, and plastics
61.43.Bn Structural modeling: serial-addition models, computer simulation

Phenomenological simulation of self-organization of microtubule driven by dynein c

Q. Chen, D. Y. Li, and K. Oiwa

J. Chem. Phys. 130, 214107 (2009); http://dx.doi.org/10.1063/1.3139300 (8 pages)

Online Publication Date: 4 June 2009

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It was recently noticed that in vitro motility assays, driven by random distributed dynein c, microtubules could form self-organized circular patterns, which could be of importance to the design of nanobiomechanical machines. In order to determine key parameters that control the self-organized movement of microtubules, a phenomenological modeling study taking account of the microtubule joining probability distribution and microtubule bias was conducted to investigate the self-organization of microtubules driven by dynein motors.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.14.E- Proteins
87.15.H- Dynamics of biomolecules
87.15.ak Monte Carlo simulations
81.16.Dn Self-assembly

Self-learning multiscale simulation for achieving high accuracy and high efficiency simultaneously

Wenfei Li and Shoji Takada

J. Chem. Phys. 130, 214108 (2009); http://dx.doi.org/10.1063/1.3146922 (6 pages) | Cited 4 times

Online Publication Date: 4 June 2009

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Biomolecular systems are inherently hierarchic and many simulation methods that try to integrate atomistic and coarse-grained (CG) models have been proposed, which are called multiscale simulations. Here, we propose a new multiscale molecular dynamics simulation method which can achieve high accuracy and high sampling efficiency simultaneously without aforehand knowledge on the CG potential and test it for a biomolecular system. In our method, a self-learning strategy is introduced to progressively improve the CG potential by an iterative way. (1) A CG model, coupled with the atomistic model, is used for obtaining CG structural ensemble, (2) which is mapped to the atomistic models. (3) The resulting atomistic ensemble is used for deriving the next-generation CG model. Two tests show that this method can rapidly improve the CG potential and achieve efficient sampling even starting from an unrealistic CG potential. The resulting free energy agreed well with the exact result and the convergence by the method was much faster than that by the replica exchange method. The method is generic and can be applied to many biological as well as nonbiological problems.
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87.15.ap Molecular dynamics simulation
87.15.B- Structure of biomolecules

Extended Lagrangian Born–Oppenheimer molecular dynamics with dissipation

Anders M. N. Niklasson, Peter Steneteg, Anders Odell, Nicolas Bock, Matt Challacombe, C. J. Tymczak, Erik Holmström, Guishan Zheng, and Valery Weber

J. Chem. Phys. 130, 214109 (2009); http://dx.doi.org/10.1063/1.3148075 (7 pages) | Cited 6 times

Online Publication Date: 4 June 2009

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Stability and dissipation in the propagation of the electronic degrees of freedom in time-reversible extended Lagrangian Born–Oppenheimer molecular dynamics [ Niklasson et al., Phys. Rev. Lett. 97, 123001 (2006) ; Phys. Rev. Lett. 100, 123004 (2008) ] are analyzed. Because of the time-reversible propagation the dynamics of the extended electronic degrees of freedom is lossless with no dissipation of numerical errors. For long simulation times under “noisy” conditions, numerical errors may therefore accumulate to large fluctuations. We solve this problem by including a dissipative external electronic force that removes noise while keeping the energy stable. The approach corresponds to a Langevin-like dynamics for the electronic degrees of freedom with internal numerical error fluctuations and external, approximately energy conserving, dissipative forces. By tuning the dissipation to balance the numerical fluctuations the external perturbation can be kept to a minimum.
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31.15.A- Ab initio calculations
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Computing vibrational energy levels by using mappings to fully exploit the structure of a pruned product basis

Jason Cooper and Tucker Carrington, Jr.

J. Chem. Phys. 130, 214110 (2009); http://dx.doi.org/10.1063/1.3140272 (7 pages) | Cited 4 times

Online Publication Date: 4 June 2009

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For the purpose of calculating (ro-)vibrational spectra, rate constants, scattering cross sections, etc. product basis sets are very popular. They, however, have the important disadvantage that they are unusably large for systems with more than four atoms. In this paper we demonstrate that it is possible to efficiently use a basis set obtained by removing, from a product basis set, functions associated with the largest diagonal Hamiltonian matrix elements. This is done by exploiting the fact that for every factor of every term in the Hamiltonian, there is a basis-set order in which the matrix representation of the factor is block diagonal. Due to this block diagonality the Lanczos algorithm can be implemented efficiently. Tests with model Hamiltonians with as many as 32 coordinates illustrate the merit of the ideas.
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33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

The confirmation of the critical point-Zeno-line similarity set from the numerical modeling data for different interatomic potentials

E. M. Apfelbaum and V. S. Vorob'ev

J. Chem. Phys. 130, 214111 (2009); http://dx.doi.org/10.1063/1.3151982 (10 pages) | Cited 6 times

Online Publication Date: 5 June 2009

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We use numerical simulation data for several model interatomic potentials to confirm the critical point-Zeno-line relations of similarity (CZS) for the liquid branch of the coexistence curve suggested earlier [ E. M. Apfelbaum and V. S. Vorob’ev, J. Phys. Chem. B 112, 13064 (2008) ]. These relations have been based on the analysis of experimental values for the critical point parameters and liquid-gas coexistence curves for a large number of real substances and two model systems. We show that the numerical modeling data as a whole confirm the CZS in the domain of the existence of liquid state. The deviations from CZS relations take place for two cases: (a) the numerically calculated coexistence curve gets into domain corresponding to solidification; (b) the liquid-vapor transition becomes metastable with respect to freezing.
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64.70.F- Liquid-vapor transitions
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Funnel hopping: Searching the cluster potential energy surface over the funnels

Longjiu Cheng, Yan Feng, Jie Yang, and Jinlong Yang

J. Chem. Phys. 130, 214112 (2009); http://dx.doi.org/10.1063/1.3152121 (7 pages) | Cited 8 times

Online Publication Date: 5 June 2009

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We designed a cluster surface smoothing method that can fast locate the minimum of the funnels in the potential energy surface (PES). By inserting the cluster surface smoothing approach into the gradient-based local optimization (LO)-phase and the global optimization (GO)-phase as a second LO-phase, the GO-phase can focus on the global information oWalesf the PES over the various funnels. Following the definition of “basin-hopping” method [D. J. and J. P. K. Doye, J. Phys. Chem. A 101, 5111 (1997) ], this method is named as “funnel hopping.” Taking a simple version of the genetic algorithm as the GO-phase, the funnel-hopping method can locate all the known putative global minima of the Lennard-Jones clusters and the extremely short-ranged Morse clusters up to cluster size N = 160 with much lower costs compared to the basin-hopping methods. Moreover the funnel-hopping method can locate the minimum of various funnels in the PES in one calculation.
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36.40.Sx Diffusion and dynamics of clusters
31.50.-x Potential energy surfaces
02.60.Pn Numerical optimization
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Non-Born–Oppenheimer electronic and nuclear wavepacket dynamics

Takehiro Yonehara, Satoshi Takahashi, and Kazuo Takatsuka

J. Chem. Phys. 130, 214113 (2009); http://dx.doi.org/10.1063/1.3151684 (14 pages) | Cited 9 times

Online Publication Date: 5 June 2009

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A practical quantum theory for unifying electronic and nuclear dynamics, which were separated by the Born–Oppenheimer approximation, is proposed. The theory consists of two processes. Nonadiabatic (quantum) electron wavepacket dynamics on branching (non-Born–Oppenheimer) nuclear paths are first constructed. Since these paths are not the classical trajectories, most of the existing semiclassical theories to generate quantum wavepacket do not work. Therefore, we apply our own developed semiclassical wavepacket theory to these generated non-Born–Oppenheimer paths. This wavepacket is generated based on what we call the action decomposed function, which does not require the information of the so-called stability matrix. Thus, the motion of nuclei is also quantized, and consequently the total wave function is represented as a series of entanglement between the electronic and nuclear wavepackets. In the last half of the article, we show the practice to demonstrate how these independent theories can be unified to give electron-nuclear wavepackets in a two-state model. The wavepackets up to the phases and resultant transition probabilities are compared to the full quantum-mechanical counterparts. It turns out that the lowest level approximation to the wavepacket approach already shows a good agreement with the full quantum quantities. Thus, the present theoretical framework gives a basic method with which to study non-Born–Oppenheimer electronic and nuclear wavepacket states relevant to ultrafast chemical events.
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03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.)
05.30.-d Quantum statistical mechanics
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

The parent anion of the RGD tripeptide: Photoelectron spectroscopy and quantum chemistry calculations

Xiang Li, Haopeng Wang, Kit H. Bowen, G. Grégoire, F. Lecomte, Jean-Pierre Schermann, and Charles Desfrançois

J. Chem. Phys. 130, 214301 (2009); http://dx.doi.org/10.1063/1.3137095 (5 pages)

Online Publication Date: 1 June 2009

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The gas-phase conformation of the intact (parent) unprotected RGD− peptide anion has been investigated using a combination of anion photoelectron spectroscopy and quantum chemistry calculations of its low-energy stable structures. The experimentally observed RGD− species correspond to a conformation in which the guanidinium group is protonated, the C-terminus is neutral, the aspartic acid carboxyl is deprotonated, and the anion’s excess electron orbital is localized on the protonated guanidinium. This structure is reminiscent of the RGD loop, which is the peptide motif recognized by trans-membrane integrins. The parent RGD− radical anion was generated using a unique infrared desorption-photoemission-helium jet ion source, whose ability to produce radical anions of peptides may also have analytical mass spectrometric implications.
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87.15.M- Spectra of biomolecules
87.15.rs Dissociation
87.15.B- Structure of biomolecules
87.14.ef Peptides
87.15.ag Quantum calculations

Investigation into the vibrational yield of OH products in the OH+H+H channel arising from the dissociative recombination of H3O+

Vitali Zhaunerchyk, Wolf D. Geppert, Stefan Rosén, Erik Vigren, Mathias Hamberg, Magdalena Kamińska, Iryna Kashperka, Magnus af Ugglas, Jacek Semaniak, Mats Larsson, and Richard D. Thomas

J. Chem. Phys. 130, 214302 (2009); http://dx.doi.org/10.1063/1.3141434 (5 pages) | Cited 3 times

Online Publication Date: 3 June 2009

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The vibrational population of the hydroxyl radical, OH, formed in the OH+H+H channel arising from the dissociative recombination of the hydronium ion, H3O+, has been investigated at the storage ring CRYRING using a position-sensitive imaging detector. Analysis shows that the OH fragments are predominantly produced in the v = 0 and v = 1 states with almost equal probabilities. This observation is in disagreement with earlier FALP experiments, which reported OH(v = 0) as the dominant product. Possible explanations for this difference are discussed.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
34.80.Lx Recombination, attachment, and positronium formation
34.80.Ht Dissociation and dissociative attachment

Coupled-cluster calculations of C2H2Si and CNHSi structural isomers

Sven Thorwirth and Michael E. Harding

J. Chem. Phys. 130, 214303 (2009); http://dx.doi.org/10.1063/1.3142702 (10 pages) | Cited 6 times

Online Publication Date: 3 June 2009

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Results of large-scale coupled-cluster calculations of selected C2H2Si and CNHSi structural isomers are reported. Equilibrium molecular structures of a total of 12 molecules in their singlet electronic states have been calculated systematically employing the coupled-cluster singles and doubles model augmented by a perturbative correction for triple excitations (CCSD(T)) in combination with Dunning’s hierarchy of correlation consistent basis sets. In addition, anharmonic force fields were calculated to yield fundamental vibrational frequencies and rotation-vibration interaction constants αiA,B,C. The latter were used to determine empirical equilibrium structures reemp of two molecules — silacyclopropenylidene, c-C2H2Si, and silapropadienylidene, H2CCSi — for which sufficient isotopic data are available from literature. Very good agreement with theoretical equilibrium structures from CCSD(T) calculations employing core-valence basis sets of quadruple and quintuple-zeta quality — i.e., cc-pwCVQZ (337 basis functions), cc-pCV5Z, and cc-pwCV5Z (581 basis functions) is found — to within 0.001 Å for bond lengths and 0.1° for bond angles. Theoretical ground state rotational constants of HSiCN and HSiNC compare very favorably with experimental microwave data from literature, to within 0.15% (HSiCN) and 0.1% (HSiNC) for the B0 and C0 rotational constants. In the case of c-C2H2Si and H2CCSi this agreement is even better than 0.1%. For the latter two molecules effects of higher-level electron-correlation and relativity to the equilibrium geometry as well as the electronic contributions to the rotational constants are investigated. For eight molecules not yet studied at high spectral resolution in the gas-phase theoretical molecular parameters are provided to support future laboratory investigations. Theoretical vibrational fundamentals compare well with data of eight species studied previously with infrared matrix isolation spectroscopy.
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33.20.Vq Vibration-rotation analysis
33.15.Dj Interatomic distances and angles
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Effects of collisions on electronic-resonance-enhanced coherent anti-Stokes Raman scattering of nitric oxide

Anil K. Patnaik, Sukesh Roy, James R. Gord, Robert P. Lucht, and Thomas B. Settersten

J. Chem. Phys. 130, 214304 (2009); http://dx.doi.org/10.1063/1.3137106 (11 pages) | Cited 3 times

Online Publication Date: 4 June 2009

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A six-level model is developed and used to study the effects of collisional energy transfer and dephasing on electronic-resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) in nitric oxide. The model includes the three levels that are coherently coupled by the three applied lasers as well as three additional bath levels that enable inclusion of the effects of electronic quenching and rotational energy transfer. The density-matrix equations that describe the evolution of the relevant populations and coherences are presented. The parametric dependencies of the ERE-CARS signal on collisional energy transfer and dephasing processes are described in terms of both a steady-state analytical solution and the numerical solutions to the governing equations. In the weak-field limit, the ERE-CARS signal scales inversely with the square of the dephasing rates for the electronic and Raman coherences. In accord with published experimental observations [Roy et al., Appl. Phys. Lett. 89, 104105 (2006)] , the ERE-CARS signal is shown to be insensitive to the collisional quenching rate. Parametric dependencies on quenching, rotational energy transfer, and pure electronic dephasing are presented, demonstrating reduced collisional dependence for saturating laser fields.
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34.50.Ez Rotational and vibrational energy transfer
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.80.-b Photon interactions with molecules

Photodissociation of (ICN)2 van der Waals dimer using velocity imaging technique

Xiao-peng Zhang, Wei-Bin Lee, Dong-feng Zhao, Ming-Kai Hsiao, Yu-Ling Chen, and King-Chuen Lin

J. Chem. Phys. 130, 214305 (2009); http://dx.doi.org/10.1063/1.3148376 (7 pages) | Cited 4 times

Online Publication Date: 4 June 2009

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Photodissociation of (ICN)2 dimer from 265 to 270 nm are studied using time-of-flight mass spectrometry combined with velocity imaging technique. Both I+ and I2+ ions are found in the mass spectra. The I2+ ions result from (1+1) resonant ionization of the neutral I2 fragment that is produced in the photodissociation of dimer, but not from dissociative ionization of (ICN)2; i.e., (ICN)2++hν→I2++2CN. The dissociation channels of I2+ leading to I+ are all found with parallel character. The total kinetic energy distributions and anisotropy parameters of the I+ channels produced by (ICN)2 are almost the same as those from a neutral I2 sample, thereby confirming that the I2 fragments are obtained in cold state. With the aid of ab initio calculations, a plausible dissociation mechanism is proposed.
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82.50.Hp Processes caused by visible and UV light
82.80.Rt Time of flight mass spectrometry
82.20.-w Chemical kinetics and dynamics

Experimental and theoretical studies of isolated neutral and ionic 2-propanol and their clusters

Joong-Won Shin and Elliot R. Bernstein

J. Chem. Phys. 130, 214306 (2009); http://dx.doi.org/10.1063/1.3148378 (11 pages) | Cited 6 times

Online Publication Date: 5 June 2009

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Infrared plus vacuum ultraviolet (IR/VUV) nonresonant photoionization spectroscopy and VUV/IR photodissociation spectroscopy are employed to study fragmentation pathways and structures of neutral and ionic 2-propanol ((CH3)2CHOH) (IPA) and their relevant clusters of size up to the pentamer. Only the gauche monomer is generated in the supersonic expansion; its VUV induced fragmentation pathways involve Cα–Cβ bond dissociation. The clusters consist of both gauche and trans conformers and their VUV induced fragmentation pathways are size dependent. The IR spectra of neutral clusters (IPA)n suggest that the dimer has a chainlike structure, whereas larger clusters have cyclic structures. VUV ionization of the neutral gauche 2-propanol generates two parent cation isomers whose Cα–Cβ bond dissociations are facilitated by excitation of the OH vibrations. The IR spectra of ionic molecular complex clusters (IPA)n−1⋅CH3CHOH+ and protonated clusters (IPA)n−1⋅H+, generated by VUV ionization of neutral clusters, show that both cluster types adopt open structures with at least one free OH group. Qualitative structural assignments are generated for the neutral species based on MP2/aug-cc-pVDZ, MP2/6-31G, and B3LYP/6-31+G(d) calculations.
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33.20.Ea Infrared spectra
36.40.Mr Spectroscopy and geometrical structure of clusters
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.20.Ni Vacuum ultraviolet spectra
31.15.E- Density-functional theory
33.20.Tp Vibrational analysis
31.15.xp Perturbation theory

Structural growth behavior and polarizability of CdnTen (n = 1–14) clusters

Jianguang Wang, Li Ma, Jijun Zhao, and Koblar Alan Jackson

J. Chem. Phys. 130, 214307 (2009); http://dx.doi.org/10.1063/1.3147519 (8 pages) | Cited 5 times

Online Publication Date: 5 June 2009

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The lowest-energy structures of CdnTen (n = 1–14) clusters have been studied by an unbiased simulated annealing search using first-principles molecular dynamics along with local optimization of “handmade” structures using density functional theory. After n ≥ 6, three-dimensional cage geometries are the lowest-energy configurations. Two families of low-lying structures, hollow cages, and endohedral or core-shell cages are found. The endohedral cages begin to appear from n = 10, and they become more energetically preferred than the hollow cages for n ≥ 12. Cd13Te13 with the core-shell cage structure is particularly stable. At the same size, the hollow cages possess smaller dipole moments and larger polarizabilities than the endohedral ones. The polarizabilities for the three-dimensional cage structures are insensitive to cluster size. The anisotropies in the polarizabilities mirror the anisotropies in cluster shapes.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Theory of long-lived nuclear spin states in solution nuclear magnetic resonance. II. Singlet spin locking

Giuseppe Pileio and Malcolm H. Levitt

J. Chem. Phys. 130, 214501 (2009); http://dx.doi.org/10.1063/1.3139064 (14 pages) | Cited 20 times

Online Publication Date: 1 June 2009

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In a previous paper [ M. Carravetta and M. H. Levitt, J. Chem. Phys. 122, 214505 (2005) ], we presented the theory of long-lived nuclear spin singlet states in low magnetic field. In this paper, we consider the spin locking of long-lived singlet states in high magnetic field by the application of resonant radio frequency irradiation. We present theoretical results for unmodulated irradiation, including approximate analytical expressions for the singlet decay rate constants. We show the results of numerical simulations, which indicate that modulated radio frequency fields may be used to achieve broadband spin locking of singlet states but only in the case of a small difference in Larmor frequencies between the members of the spin pair.
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76.60.Es Relaxation effects

Molecular dynamics of glycerol and glycerol-trehalose bioprotectant solutions nanoconfined in porous silicon

R. Busselez, R. Lefort, M. Guendouz, B. Frick, O. Merdrignac-Conanec, and D. Morineau

J. Chem. Phys. 130, 214502 (2009); http://dx.doi.org/10.1063/1.3147222 (9 pages) | Cited 5 times

Online Publication Date: 2 June 2009

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Glycerol and trehalose-glycerol binary solutions are glass-forming liquids with remarkable bioprotectant properties. Incoherent quasielastic neutron scattering is used to reveal the different effects of nanoconfinement and addition of trehalose on the molecular dynamics in the normal liquid and supercooled liquid phases, on a nanosecond time scale. Confinement has been realized in straight channels of diameter D = 8 nm formed by porous silicon. It leads to a faster and more inhomogeneous relaxation dynamics deep in the liquid phase. This confinement effect remains at lower temperature where it affects the glassy dynamics. The glass transitions of the confined systems are shifted to low temperature with respect to the bulk ones. Adding trehalose tends to slow down the overall glassy dynamics and increases the nonexponential character of the structural relaxation. Unprecedented results are obtained for the binary bioprotectant solution, which exhibits an extremely non-Debye relaxation dynamics as a result of the combination of the effects of confinement and mixing of two constituents.
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61.20.Ja Computer simulation of liquid structure
64.70.pm Liquids
61.25.Em Molecular liquids
61.43.Gt Powders, porous materials

Electronic properties of potassium doped FePc from electron energy-loss spectroscopy

A. König, F. Roth, R. Kraus, and M. Knupfer

J. Chem. Phys. 130, 214503 (2009); http://dx.doi.org/10.1063/1.3146812 (5 pages) | Cited 5 times

Online Publication Date: 2 June 2009

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We have studied the electronic structure of potassium doped iron phthalocyanine (FePc) phases using electron energy-loss spectroscopy. The electronic excitation spectrum of FePc is rather complex and comprises both π-π∗ transitions of the phthalocyanine ligand and transitions that involve the Fe 3d orbitals. This allows deeper insight into the orbital occupation in FePc. Potassium doping, i.e., the addition of electrons to the FePc molecules causes significant changes in the electronic excitations, which signal filling of π∗ as well as Fe 3d orbitals.
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71.20.Rv Polymers and organic compounds
79.20.Uv Electron energy loss spectroscopy
61.72.up Other materials
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