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 Aug 2011

Volume 135, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 135, 050901 (2011); http://dx.doi.org/10.1063/1.3615063 (8 pages)

George W. Flynn
Enlarge Image | Read More
Page 1 of 3 Pages Next Page | Jump to Page
back to top
RSS Feeds
FREE

Perspective: The dawning of the age of graphene

George W. Flynn

J. Chem. Phys. 135, 050901 (2011); http://dx.doi.org/10.1063/1.3615063 (8 pages) | Cited 1 time

Online Publication Date: 1 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Graphene is a single sheet of carbon atoms that constitutes the basic building block of macroscopic graphite crystals. Held together by a backbone of overlapping sp2 hybrids, graphene's 2p orbitals form π state bands that delocalize over an entire 2-dimensional macroscopic carbon sheet leading to a number of unusual characteristics that include large electrical and thermal conductivities. Recent discoveries have provided simple methods (e.g., mechanical cleavage of graphite) for preparing laboratory scale samples that can be used to investigate the fundamental physical and chemical characteristics of graphene. In addition, a number of techniques have emerged that show promise for producing large-scale samples with the ultimate goal of developing devices that take advantage of graphene's unusual properties. As large samples become available, the possibility grows for applications of this material in solar cell technology (as flexible, transparent electrodes), in composite material development, and in electronic devices.
Show PACS
61.48.Gh Structure of graphene
65.80.Ck Thermal properties of graphene
back to top
RSS Feeds
FREE

Communication: Effective temperature and glassy dynamics of active matter

Shenshen Wang and Peter G. Wolynes

J. Chem. Phys. 135, 051101 (2011); http://dx.doi.org/10.1063/1.3624753 (4 pages) | Cited 1 time

Online Publication Date: 4 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A systematic expansion of the many-body master equation for active matter, in which motors power configurational changes as in the cytoskeleton, is shown to yield a description of the steady state and responses in terms of an effective temperature. The effective temperature depends on the susceptibility of the motors and a Peclet number which measures their strength relative to thermal Brownian diffusion. The analytic prediction is shown to agree with previous numerical simulations and experiments. The mapping also establishes a description of aging in active matter that is also kinetically jammed.
Show PACS
05.40.Jc Brownian motion
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

A new internally contracted multi-reference configuration interaction method

K. R. Shamasundar, Gerald Knizia, and Hans-Joachim Werner

J. Chem. Phys. 135, 054101 (2011); http://dx.doi.org/10.1063/1.3609809 (17 pages) | Cited 1 time

Online Publication Date: 1 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a new internally contracted multi-reference configuration interaction (MRCI) method which, at the same time, efficiently handles large active orbital spaces, long configuration expansions, and many closed-shell orbitals in the reference function. This is achieved by treating the closed-shell orbitals explicitly, so that all required coupling coefficients and density matrices only depend on active orbital labels. As a result, closed-shell orbitals are handled as efficiently as in a closed-shell single-reference program, and this opens up the possibility to perform high-accuracy MRCI calculations for much larger molecules than before. The enormously complex equations are derived using a new domain-specific computer algebra system and semi-automatically implemented using a newly developed integrated tensor framework. The accuracy and efficiency of the MRCI method is demonstrated with applications to dioxygen-copper complexes with different ligands, some of which involve more than 30 atoms, and to spin-state splittings of ferrocene.
Show PACS
31.15.vq Electron correlation calculations for polyatomic molecules

Soret motion in non-ionic binary molecular mixtures

Yves Leroyer and Alois Würger

J. Chem. Phys. 135, 054102 (2011); http://dx.doi.org/10.1063/1.3615954 (7 pages)

Online Publication Date: 1 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We study the Soret coefficient of binary molecular mixtures with dispersion forces. Relying on standard transport theory for liquids, we derive explicit expressions for the thermophoretic mobility and the Soret coefficient. Their sign depends on composition, the size ratio of the two species, and the ratio of Hamaker constants. Our results account for several features observed in experiment, such as a linear variation with the composition; they confirm the general rule that small molecules migrate to the warm, and large ones to the cold.
Show PACS
66.10.cd Thermal diffusion and diffusive energy transport
61.25.Em Molecular liquids

Quantum optimal control for the full ensemble of randomly oriented molecules having different field-free Hamiltonians

Yuzuru Kurosaki, Akira Ichihara, and Keiichi Yokoyama

J. Chem. Phys. 135, 054103 (2011); http://dx.doi.org/10.1063/1.3618719 (6 pages)

Online Publication Date: 1 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have presented the optimal control theory formulation to calculate optimal fields that can control the full ensemble of randomly oriented molecules having different field-free Hamiltonians. The theory is applied to the fifty-fifty mixture of randomly oriented 133CsI and 135CsI isotopomers and an optimal field is sought to achieve isotope-selective vibrational excitations with high efficiency. Rotational motion is frozen and two total times (T’s) of electric field duration, 460 000 and 920 000 a.u. (11.1 and 22.2 ps), are chosen in the present calculation. As a result, the final yields for T = 460 000 and 920 000 a.u. are calculated to be 0.706 and 0.815, respectively. The relatively high final yield obtained for T = 920 000 a.u. strongly suggests that a single laser pulse can control the full ensemble of randomly oriented non-identical molecules. The result is quite encouraging in terms of the application to isotope-separation processes.
Show PACS
31.30.Gs Hyperfine interactions and isotope effects
32.10.Bi Atomic masses, mass spectra, abundances, and isotopes
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Be Level crossing and optical pumping
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Inherent structures for soft long-range interactions in two-dimensional many-particle systems

Robert D. Batten, Frank H. Stillinger, and Salvatore Torquato

J. Chem. Phys. 135, 054104 (2011); http://dx.doi.org/10.1063/1.3615527 (16 pages)

Online Publication Date: 2 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We generate inherent structures, local potential-energy minima, of the “k-space overlap potential” in two-dimensional many-particle systems using a cooling and quenching simulation technique. The ground states associated with the k-space overlap potential are stealthy (i.e., completely suppress single scattering of radiation for a range of wavelengths) and hyperuniform (i.e., infinite wavelength density fluctuations vanish). However, we show via quantitative metrics that the inherent structures exhibit a range of stealthiness and hyperuniformity depending on the fraction of degrees of freedom χ that are constrained. Inherent structures in two dimensions typically contain five-particle rings, wavy grain boundaries, and vacancy-interstitial defects. The structural and thermodynamic properties of the inherent structures are relatively insensitive to the temperature from which they are sampled, signifying that the energy landscape is relatively flat along the directions sampled, with wide shallow local minima and devoid of deep wells. Using the nudged-elastic-band algorithm, we construct paths from ground-state configurations to inherent structures and identify the transition points between them. In addition, we use point patterns generated from a random sequential addition (RSA) of hard disks, which are nearly stealthy, and examine the particle rearrangements necessary to make the configurations absolutely stealthy. We introduce a configurational proximity metric to show that only small local, but collective, particle rearrangements are needed to drive initial RSA configurations to stealthy disordered ground states. These results lead to a more complete understanding of the unusual behaviors exhibited by the family of “collective-coordinate” potentials to which the k-space overlap potential belongs.
Show PACS
05.20.Jj Statistical mechanics of classical fluids
05.70.Ce Thermodynamic functions and equations of state
05.45.-a Nonlinear dynamics and chaos
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Time-dependent density functional theory excited state nonadiabatic dynamics combined with quantum mechanical/molecular mechanical approach: Photodynamics of indole in water

Matthias Wohlgemuth, Vlasta Bonačić-Koutecký, and Roland Mitrić

J. Chem. Phys. 135, 054105 (2011); http://dx.doi.org/10.1063/1.3622563 (10 pages)

Online Publication Date: 3 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a combination of time-dependent density functional theory with the quantum mechanical/molecular mechanical approach which can be applied to study nonadiabatic dynamical processes in molecular systems interacting with the environment. Our method is illustrated on the example of ultrafast excited state dynamics of indole in water. We compare the mechanisms of nonradiative relaxation and the electronic state lifetimes for isolated indole, indole in a sphere of classical water, and indole + 3H2O embedded in a classical water sphere. In the case of isolated indole, the initial excitation to the S2 electronic state is followed by an ultrafast internal conversion to the S1 state with a time constant of 17 fs. The S1 state is long living (>30 ps) and deactivates to the ground state along the N–H stretching coordinate. This deactivation mechanism remains unchanged for indole in a classical water sphere. However, the lifetimes of the S2 and S1 electronic states are extended. The inclusion of three explicit water molecules opens a new relaxation channel which involves the electron transfer to the solvent, leading eventually to the formation of a solvated electron. The relaxation to the ground state takes place on a time scale of 60 fs and contributes to the lowering of the fluorescence quantum yield. Our simulations demonstrate the importance of including explicit water molecules in the theoretical treatment of solvated systems.
Show PACS
31.15.ee Time-dependent density functional theory
31.70.Dk Environmental and solvent effects
33.50.Dq Fluorescence and phosphorescence spectra
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Alternative wavefunction ansatz for including explicit electron-proton correlation in the nuclear-electronic orbital approach

Chaehyuk Ko, Michael V. Pak, Chet Swalina, and Sharon Hammes-Schiffer

J. Chem. Phys. 135, 054106 (2011); http://dx.doi.org/10.1063/1.3611054 (13 pages) | Cited 2 times

Online Publication Date: 3 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The nuclear-electronic orbital (NEO) approach treats specified nuclei quantum mechanically on the same level as the electrons with molecular orbital techniques. The explicitly correlated Hartree-Fock (NEO-XCHF) approach was developed to incorporate electron-nucleus dynamical correlation directly into the variational optimization of the nuclear-electronic wavefunction. In the original version of this approach, the Hartree-Fock wavefunction is multiplied by (1+math), where math is a geminal operator expressed as a sum of Gaussian type geminal functions that depend on the electron-proton distance. Herein, a new wavefunction ansatz is proposed to avoid the computation of five- and six-particle integrals and to simplify the computation of the lower dimensional integrals involving the geminal functions. In the new ansatz, denoted NEO-XCHF2, the Hartree-Fock wavefunction is multiplied by math rather than (1+math). Although the NEO-XCHF2 ansatz eliminates the integrals that are quadratic in the geminal functions, it introduces terms in the kinetic energy integrals with no known analytical solution. A truncated expansion scheme is devised to approximate these problematic terms. An alternative hybrid approach, in which the kinetic energy terms are calculated with the original NEO-XCHF ansatz and the potential energy terms are calculated with the NEO-XCHF2 ansatz, is also implemented. Applications to a series of model systems with up to four electrons provide validation for the NEO-XCHF2 approach and the treatments of the kinetic energy terms.
Show PACS
31.50.-x Potential energy surfaces
31.15.xt Variational techniques
31.15.xr Self-consistent-field methods
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.B- Approximate calculations

Rigorous coarse-graining for the dynamics of linear systems with applications to relaxation dynamics in proteins

Reza Soheilifard, Dmitrii E. Makarov, and Gregory J. Rodin

J. Chem. Phys. 135, 054107 (2011); http://dx.doi.org/10.1063/1.3613678 (10 pages) | Cited 1 time

Online Publication Date: 4 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Reduced-dimensionality, coarse-grained models are commonly employed to describe the structure and dynamics of large molecular systems. In those models, the dynamics is often described by Langevin equations of motion with phenomenological parameters. This paper presents a rigorous coarse-graining method for the dynamics of linear systems. In this method, as usual, the conformational space of the original atomistic system is divided into master and slave degrees of freedom. Under the assumption that the characteristic timescales of the masters are slower than those of the slaves, the method results in Langevin-type equations of motion governed by an effective potential of mean force. In addition, coarse-graining introduces hydrodynamic-like coupling among the masters as well as non-trivial inertial effects. Application of our method to the long-timescale part of the relaxation spectra of proteins shows that such dynamic coupling is essential for reproducing their relaxation rates and modes.
Show PACS
87.15.hm Folding dynamics
87.15.hp Conformational changes
36.20.Ey Conformation (statistics and dynamics)
87.15.La Mechanical properties
87.14.E- Proteins
87.15.hj Transport dynamics

Ab initio quantum Monte Carlo study of the binding of a positron to alkali-metal hydrides

Yukiumi Kita, Ryo Maezono, Masanori Tachikawa, Mike D. Towler, and Richard J. Needs

J. Chem. Phys. 135, 054108 (2011); http://dx.doi.org/10.1063/1.3620151 (5 pages) | Cited 1 time

Online Publication Date: 4 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Quantum Monte Carlo methods are used to investigate the binding of a positron to the alkali-metal hydrides, XH (X = Na and K). We obtain positron affinities for the NaH and KH molecules of 1.422(10) eV and 2.051(39) eV, respectively. These are considerably larger than the previous results of 1.035 eV and 1.273 eV obtained from multireference single- and double-excitation configuration interaction calculations. Together with our previous results for [LiH;e+] [Y. Kita et al., J. Chem. Phys. 131, 134310 (2009)], our study confirms the strong correlation between the positron affinity and dipole moment of alkali-metal hydrides.
Show PACS
34.80.Uv Positron scattering
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.A- Ab initio calculations

Fractional spin in reduced density-matrix functional theory

N. Helbig, G. Theodorakopoulos, and N. N. Lathiotakis

J. Chem. Phys. 135, 054109 (2011); http://dx.doi.org/10.1063/1.3615955 (9 pages) | Cited 1 time

Online Publication Date: 5 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We study the behavior of different functionals of the one-body reduced density matrix (1RDM) for systems with fractional z-component of the total spin. We define these systems as ensembles of integer spin states. It is shown that, similarly to density functional theory, the error in the dissociation of diatomic molecules is directly related to the deviation from constancy of the atomic total energies as functions of the fractional spin. However, several functionals of the 1RDM show a size inconsistency which leads to additional errors. We also investigate the difference between a direct evaluation of the energy of an ensemble of integer-spin systems and a direct minimization of the energy of a fractional-spin system.
Show PACS
31.15.E- Density-functional theory
33.15.Fm Bond strengths, dissociation energies
back to top Advanced Experimental Techniques
FREE

Nuclear magnetic relaxation in water revisited

Stefan Hartwig, Jens Voigt, Hans-Jürgen Scheer, Hans-Helge Albrecht, Martin Burghoff, and Lutz Trahms

J. Chem. Phys. 135, 054201 (2011); http://dx.doi.org/10.1063/1.3623024 (4 pages) | Cited 1 time

Online Publication Date: 5 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this study, we revisited nuclear magnetic relaxation of 1H in water at very low Larmor frequencies that has been studied intensively in earlier years. We make use of the recently developed superconducting quantum interference device based ultra-low field NMR technique, which enables much easier access to the longitudinal spin-lattice relaxation time T1 and the transversal spin-spin relaxation time T2 below several kHz than traditional field cycling methods. Our data reproduce and complement the earlier results, in that they corroborate the finding of an exchange process with a correlation time of about 0.34 ms at room temperature which can be attributed to the migration of hydronium and hydroxyl ions in neutral water via hydrogen bridges. The corresponding relaxation process is driven by the interaction of the protons with 17O and contributes to the T1 and the T2 relaxation rate by about 0.12 s−1. In addition, we found evidence of a very slow exchange process at about 100 Hz that has hitherto not been reported.
Show PACS
76.60.Es Relaxation effects
85.25.Dq Superconducting quantum interference devices (SQUIDs)
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Least-squares analysis of overlapped bound-free absorption spectra and predissociation data in diatomics: The C(1Πu) state of I2

Joel Tellinghuisen

J. Chem. Phys. 135, 054301 (2011); http://dx.doi.org/10.1063/1.3616039 (11 pages)

Online Publication Date: 1 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Absorption spectra are recorded at low resolution but high quantitative precision for I2 vapor at 35 °C and 64 °C. These and literature spectra are analyzed by least-squares quantum spectral simulation of the overlapped A ← X, B ← X, and C(1Πu) ← X transitions, with the aid of a pseudocontinuum model for the discrete regions of the A ← X and B ← X spectra. The analysis yields improved descriptions of the small-R regions of the A- and B-state potentials, which are known precisely at larger R from discrete spectroscopy. The C potential is determined at small R from its C ← X absorption, at intermediate R from literature data for B → C predissociation, and at large R from its known van der Waals well. The estimates of the electronic transition moment function |μe(R)| for the B–X transition expand upon precise results from a recent determination by a different method. For the C–X and A–X transitions, the R-dependence of the transition moment functions resembles that found previously for these systems in Br2. Of the spectroscopic properties, the C ← X spectrum is most altered from the previous analysis, being now ∼20% weaker. For B → C predissociation, no derived C potential has yielded computed rates in adequate statistical agreement with the analyzed experimental data.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.20.Kf Visible spectra
33.20.Lg Ultraviolet spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
34.20.Gj Intermolecular and atom-molecule potentials and forces

Collision limited reaction rates for arbitrarily shaped particles across the entire diffusive Knudsen number range

Ranganathan Gopalakrishnan, Thaseem Thajudeen, and Christopher J. Hogan, Jr.

J. Chem. Phys. 135, 054302 (2011); http://dx.doi.org/10.1063/1.3617251 (9 pages) | Cited 1 time

Online Publication Date: 1 August 2011

Full Text: Read Online (HTML) | Download PDF


See Also: Erratum

Show Abstract
Aerosol particle reactions with vapor molecules and molecular clusters are often collision rate limited, hence determination of particle-vapor molecule and particle-molecular cluster collision rates are of fundamental importance. These collisions typically occur in the mass transfer transition regime, wherein the collision kernel (collision rate coefficient) is dependent upon the diffusive Knudsen number, KnD. While this alone prohibits analytical determination of the collision kernel, aerosol particle- vapor molecule collisions are further complicated when particles are non-spherical, as is often the case for particles formed in high temperature processes (combustion). Recently, through a combination of mean first passage time simulations and dimensional analysis, it was shown that the collision kernel for spherical particles and vapor molecules could be expressed as a dimensionless number, H, which is solely a function of KnD. In this work, it is shown through similar mean first passage times and redefinitions of H and KnD that the H(KnD) relationship found for spherical particles applies for particles of arbitrary shape, including commonly encountered agglomerate particles. Specifically, it is shown that to appropriately define H and KnD, two geometric descriptors for a particle are necessary: its Smoluchowski radius, which defines the collision kernel in the continuum regime (KnD→0) and its orientationally averaged projected area, which defines the collision kernel in the free molecular regime (KnD→∞). With these two parameters, as well as the properties of the colliding vapor molecule (mass and diffusion coefficient), the particle-vapor molecule collision kernel in the continuum, transition, and free molecular regimes can be simply calculated using the H(KnD) relationship.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Wt Computational modeling; simulation
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Db Transition state theory and statistical theories of rate constants
82.70.Rr Aerosols and foams
82.40.Ck Pattern formation in reactions with diffusion, flow and heat transfer

Full-dimensional multi configuration time dependent Hartree calculations of the ground and vibrationally excited states of He2,3Br2 clusters

Álvaro Valdés, Rita Prosmiti, Pablo Villarreal, and Gerardo Delgado-Barrio

J. Chem. Phys. 135, 054303 (2011); http://dx.doi.org/10.1063/1.3618727 (9 pages) | Cited 1 time

Online Publication Date: 1 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Quantum dynamics calculations are reported for the tetra-, and penta-atomic van der Waals HeNBr2 complexes using the multiconfiguration time-dependent Hartree (MCTDH) method. The computations are carried out in satellite coordinates, and the kinetic energy operator in this set of coordinates is given. A scheme for the representation of the potential energy surface based on the sum of the three-body HeBr2 interactions at CSSD(T) level plus the He-He interaction is employed. The potential surfaces show multiple close lying minima, and a quantum description of such highly floppy multiminima systems is presented. Benchmark, full-dimensional converged results on ground vibrational/zero-point energies are reported and compared with recent experimental data available for all these complexes, as well as with previous variational quantum calculations for the smaller HeBr2 and He2Br2 complexes on the same surface. Some low-lying vibrationally excited eigenstates are also computed by block improved relaxation calculations. The binding energies and the corresponding vibrationally averaged structures are determined for different conformers of these complexes. Their relative stability is discussed, and contributes to evaluate the importance of the multiple-minima topology of the underlying potential surface.
Show PACS
31.15.xr Self-consistent-field methods
31.50.Df Potential energy surfaces for excited electronic states
33.15.Bh General molecular conformation and symmetry; stereochemistry
34.20.Gj Intermolecular and atom-molecule potentials and forces
36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.bw Coupled-cluster theory

Revisiting falloff curves of thermal unimolecular reactions

J. Troe and V. G. Ushakov

J. Chem. Phys. 135, 054304 (2011); http://dx.doi.org/10.1063/1.3615542 (10 pages)

Online Publication Date: 1 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Master equations for thermal unimolecular reactions and the reverse thermal recombination reactions are solved for a series of model reaction systems and evaluated with respect to broadening factors. It is shown that weak collision center broadening factors Fcentwc can approximately be related to the collision efficiencies βc through a relation Fcentwc ≈ max {βc0.14, 0.64(±0.03)}. In addition, it is investigated to what extent weak collision falloff curves in general can be expressed by the limiting low and high pressure rate coefficients together with central broadening factors Fcent only. It is shown that there cannot be one “best” analytical expression for broadening factors F(x) as a function of the reduced pressure scale x = k0/k∞. Instead, modelled falloff curves of various reaction systems, for given k0, k∞, and Fcent, fall into a band of about 10% width in F(x). A series of analytical expressions for F(x), from simple symmetric to more elaborate asymmetric broadening factors, are compared and shown to reproduce the band of modelled broadening factors with satisfactory accuracy.
Show PACS
82.20.Wt Computational modeling; simulation
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Fd Collision theories; trajectory models

Geometrical structure of benzene and naphthalene: Ultrahigh-resolution laser spectroscopy and ab initio calculation

Masaaki Baba, Yasuyuki Kowaka, Umpei Nagashima, Takayoshi Ishimoto, Hitoshi Goto, and Naofumi Nakayama

J. Chem. Phys. 135, 054305 (2011); http://dx.doi.org/10.1063/1.3622766 (5 pages) | Cited 1 time

Online Publication Date: 2 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Geometrical structures of the isolated benzene and naphthalene molecules have been accurately determined by using ultrahigh-resolution laser spectroscopy and ab initio calculation in a complementary manner. The benzene molecule has been identified to be planar and hexagonal (D6h) and the structure has been determined with accuracies of 2 × 10−14 m (0.2 mÅ; 1 Å = 1 × 10−10 m) for the C–C bond length and 1.0 × 10−13 m (1.0 mÅ) for the C–H bond length. The naphthalene molecule has been identified to be symmetric with respect to three coordinate axes (D2h) and the structure has been determined with comparable accuracies. We discuss the effect of vibrational averaging that is a consequence of zero-point motions on the uncertainty in determining the bond lengths.
Show PACS
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
31.15.ae Electronic structure and bonding characteristics

Pressure and temperature dependence of dissociative and non-dissociative electron attachment to CF3: Experiments and kinetic modeling

Nicholas S. Shuman, Thomas M. Miller, Jeffrey F. Friedman, Albert A. Viggiano, Anatol I. Maergoiz, and Jürgen Troe

J. Chem. Phys. 135, 054306 (2011); http://dx.doi.org/10.1063/1.3614471 (10 pages) | Cited 1 time

Online Publication Date: 3 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The kinetics of electron attachment to CF3 as a function of temperature (300–600 K) and pressure (0.75–2.5 Torr) were studied by variable electron and neutral density attachment mass spectrometry exploiting dissociative electron attachment to CF3Br as a radical source. Attachment occurs through competing dissociative (CF3 + e− → CF2 + F−) and non-dissociative channels (CF3 + e− → CF3−). The rate constant of the dissociative channel increases strongly with temperature, while that of the non-dissociative channel decreases. The rate constant of the non-dissociative channel increases strongly with pressure, while that of the dissociative channel shows little dependence. The total rate constant of electron attachment increases with temperature and with pressure. The system is analyzed by kinetic modeling in terms of statistical theory in order to understand its properties and to extrapolate to conditions beyond those accessible in the experiment.
Show PACS
34.80.Ht Dissociation and dissociative attachment
33.15.Ta Mass spectra
34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)

Experimental and theoretical studies of neutral MgmCnHx and BemCnHx clusters

Feng Dong, Yan Xie, and Elliot R. Bernstein

J. Chem. Phys. 135, 054307 (2011); http://dx.doi.org/10.1063/1.3617571 (6 pages)

Online Publication Date: 3 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Neutral MgmCnHx and BemCnHx clusters are investigated both experimentally and theoretically for the first time. Single photon ionization at 193 nm is used to detect neutral cluster distributions through time of flight mass spectrometry. MgmCnHx and BemCnHx clusters are generated through laser ablation of Mg or Be foil into CH4/He expansion gas. A number of members of each cluster series are identified through isotopic substitution experiments employing 13CH4 and CD4 instead of CH4 in the expansion gas. An oscillation of the vertical ionization energies (VIEs) of MgmCnHx clusters is observed in the experiments. The VIEs of MgmCnHx clusters are observed to vary as a function of the number of H atoms in the clusters. Density functional theory (DFT) and ab initio (MP2) calculations are carried out to explore the structures and ionization energies of MgmCnHx clusters. Many BemCnHx clusters are also generated and detected in the experiments. The structures and VIEs of BemCnHx clusters are also studied by theoretical calculations. Calculational results provide a good and consistent explanation for the experimental observations, and are in general agreement with them for both series of clusters.
Show PACS
36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.A- Ab initio calculations
31.15.E- Density-functional theory
33.15.Ta Mass spectra
33.80.Eh Autoionization, photoionization, and photodetachment

Ultrafast dynamics of aniline in the 294-234 nm excitation range: The role of the πσ* state

Raúl Montero, Álvaro Peralta Conde, Virginia Ovejas, Roberto Martínez, Fernando Castaño, and Asier Longarte

J. Chem. Phys. 135, 054308 (2011); http://dx.doi.org/10.1063/1.3615544 (8 pages)

Online Publication Date: 3 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The ultrafast relaxation of jet-cooled aniline was followed by time-resolved ionization, after excitation in the 294-234 interval. The studied range of energy covers the absorption of the two bright ππ* excitations, S1 and S3, and the almost dark S2 (πσ*) state. The employed probe wavelengths permit to identify different ultrafast time constants related with the coupling of the involved electronic surfaces. A τ1 = 165 ± 30 fs lifetime is attributed to dynamics along the S2 (πσ*) repulsive surface. Other relaxation channels as the S1→S0 and S3→S1 internal conversion are also identified and characterized. The work provides a general view of the photophysics of aniline, particularly regarding the role of the πσ* state. This state appears as minor dissipation process due to the ineffective coupling with the bright S1 and S3 states, being the S1→S0 internal conversion the main non-radiative process in the full studied energy range. Additionally, the influence of the off-resonance adiabatic excitation of higher energy electronic states, particularly S3, is also observed and discussed.
Show PACS
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Lg Ultraviolet spectra
33.50.Hv Radiationless transitions, quenching

Electronic spectroscopy of the previously unknown arsenic carbide (AsC) free radical

Jie Yang and Dennis J. Clouthier

J. Chem. Phys. 135, 054309 (2011); http://dx.doi.org/10.1063/1.3618955 (6 pages) | Cited 1 time

Online Publication Date: 4 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The previously unknown arsenic carbide (AsC) free radical has been identified in the gas phase through a combination of laser-induced fluorescence (LIF), single vibronic level emission, and stimulated emission pumping (SEP) spectroscopy in a supersonic expansion. The As12C and As13C isotopologues have been detected as products of an electric discharge in mixtures of arsine (AsH3) and carbon dioxide (12CO2 or 13CO2) in high pressure argon. The B 2Σ+-X 2Σ+ band system was recorded by LIF spectroscopy and emission transitions from the B state down to the ground state and to the low-lying A 2Πi state were observed. High resolution studies of the B−X 0–0 band by LIF and the B−A 0–0 band by SEP spectroscopy enabled a determination of the molecular structures in the three states. Although CN, CP, and AsC have similar X 2Σ+ and A 2Πi. states, the B 2Σ+ state molecular orbital configuration of CP and AsC differs from that of the CN free radical.
Show PACS
33.50.Dq Fluorescence and phosphorescence spectra
33.80.Be Level crossing and optical pumping
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Relativistic contributions to single and double core electron ionization energies of noble gases

J. Niskanen, P. Norman, H. Aksela, and H. Ågren

J. Chem. Phys. 135, 054310 (2011); http://dx.doi.org/10.1063/1.3621833 (6 pages) | Cited 1 time

Online Publication Date: 5 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have performed relativistic calculations of single and double core 1s hole states of the noble gas atoms in order to explore the relativistic corrections and their additivity to the ionization potentials. Our study unravels the interplay of progression of relaxation, dominating in the single and double ionization potentials of the light elements, versus relativistic one-electron effects and quantum electrodynamic effects, which dominate toward the heavy end. The degree of direct relative additivity of the relativistic corrections for the single electron ionization potentials to the double electron ionization potentials is found to gradually improve toward the heavy elements. The Dirac–Coulomb Hamiltonian is found to predict a scaling ratio of ∼4 for the relaxation induced relativistic energies between double and single ionization. Z-scaling of the computed quantities were obtained by fitting to power law. The effects of nuclear size and form were also investigated and found to be small. The results indicate that accurate predictions of double core hole ionization potentials can now be made for elements across the full periodic table.
Show PACS
31.30.jc Relativistic corrections to atomic structure and properties
32.80.Aa Inner-shell excitation and ionization
32.50.+d Fluorescence, phosphorescence (including quenching)
32.80.Rm Multiphoton ionization and excitation to highly excited states
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

Energy transfer of highly vibrationally excited naphthalene: Collisions with CHF3, CF4, and Kr

Hsu Chen Hsu, Ming-Tsang Tsai, Yuri A. Dyakov, and Chi-Kung Ni

J. Chem. Phys. 135, 054311 (2011); http://dx.doi.org/10.1063/1.3622765 (5 pages)

Online Publication Date: 5 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Energy transfer of highly vibrationally excited naphthalene in the triplet state in collisions with CHF3, CF4, and Kr was studied using a crossed-beam apparatus along with time-sliced velocity map ion imaging techniques. Highly vibrationally excited naphthalene (2.0 eV vibrational energy) was formed via the rapid intersystem crossing of naphthalene initially excited to the S2 state by 266 nm photons. The shapes of the collisional energy-transfer probability density functions were measured directly from the scattering results of highly vibrationally excited naphthalene. In comparison to Kr atoms, the energy transfer in collisions between CHF3 and naphthalene shows more forward scatterings, larger cross section for vibrational to translational (V → T) energy transfer, smaller cross section for translational to vibrational and rotational (T → VR) energy transfer, and more energy transferred from vibration to translation, especially in the range −ΔEd = −100 to −800 cm−1. On the other hand, the difference of energy transfer properties between collisional partners Kr and CF4 is small. The enhancement of the V → T energy transfer in collisions with CHF3 is attributed to the large attractive interaction between naphthalene and CHF3 (1–3 kcal/mol).
Show PACS
34.50.Ez Rotational and vibrational energy transfer
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis

Delocalized electronic behavior observed in transition metal oxide clusters under strong-field excitation

Scott G. Sayres, Matt W. Ross, and A. W. Castleman, Jr.

J. Chem. Phys. 135, 054312 (2011); http://dx.doi.org/10.1063/1.3617231 (7 pages)

Online Publication Date: 5 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Heterogeneously composed clusters are exposed to intensity resolved, 100 fs laser pulses to reveal the energy requirements for the production of the high charge states of both metal and nonmetal ions. The ionization and fragmentation of group V transition metal oxide clusters are here examined with laser intensities ranging nearly four orders in magnitude (∼3 × 1011 W/cm2 to ∼2 × 1015 W/cm2) at 624 nm. The ionization potentials of the metal atoms are measured using both multiphoton ionization and tunneling ionization models. We demonstrate that the intensity selective scanning method can be utilized to measure the low ionization potentials of transition metals (∼7 eV). The high charge states demonstrate an enhancement in ionization that is three orders of magnitude lower in laser intensity than predicted for the atomic counterparts. Finally, the response from the various metals and the oxygen is compared to elucidate the mechanism of enhanced ionization that is observed. Specifically, the sequence of ion appearances demonstrates delocalized electron behavior over the entire cluster.
Show PACS
36.40.Cg Electronic and magnetic properties of clusters
36.40.Wa Charged clusters
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
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

Small polaron hopping conduction mechanism in Fe doped LaMnO3

Wasi Khan, Alim H. Naqvi, Maneesha Gupta, Shahid Husain, and Ravi Kumar

J. Chem. Phys. 135, 054501 (2011); http://dx.doi.org/10.1063/1.3615720 (6 pages)

Online Publication Date: 1 August 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The structural and electrical transport properties of LaMn1−xFexO3 (0.1 ≤ x ≤ 0.6) bulk samples have been investigated. The powder x-ray diffraction patterns at room temperature show that all samples are formed in single phase. The temperature dependent resistivity data have been fitted with the Mott's variable-range hopping (VRH) model for an entire studied range of the temperature (77–300 K) to calculate the hopping distance (Rh) and the density of states at Fermi level (N(EF)). It is found that all parameters vary systematically with the increase in Fe concentration. Moreover, the resistivity data were also fitted in the small polaron hopping (SPH) model. The non-adiabatic SPH conduction mechanism is followed by all samples. This type conduction mechanism is far accompanied by subtle electronically induced structural changes involving in Fe–O–Fe and Fe–O–Mn bond angles and bond lengths. Thus we suggest that the transport properties can be explained according to the additional localization of charge carriers induced by Fe doping.
Show PACS
72.20.Ee Mobility edges; hopping transport
71.38.-k Polarons and electron-phonon interactions
61.66.Fn Inorganic compounds
72.80.Sk Insulators
71.20.Ps Other inorganic compounds
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. The submersion of sodium clusters in helium nanodroplets: Identification of the surface → interior transition
  2. Note: Accurate ab initio predictions of ionization energies of propargyl and allyl radicals: Revisited
  3. Conformational fluctuations of a protein–DNA complex and the structure and ordering of water around it
  4. A two-dimensional-reference interaction site model theory for solvation structure near solid-liquid interface
  5. Thermal fluctuations in shape, thickness, and molecular orientation in lipid bilayers
Go to AIP Home
Copyright © American Institute of Physics
close