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28 May 2013

Volume 138, Issue 20 (partial)

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J. Chem. Phys. 138, 204901 (2013); http://dx.doi.org/10.1063/1.4804270 (16 pages)

Mattia Felice Palermo, Antonio Pizzirusso, Luca Muccioli, and Claudio Zannoni
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back to top Atoms, Molecules, and Clusters

Correlation between a photoelectron and a fragment ion in dissociative ionization of ethanol in intense near-infrared laser fields

Kouichi Hosaka, Atsushi Yokoyama, Kaoru Yamanouchi, and Ryuji Itakura

J. Chem. Phys. 138, 204301 (2013); http://dx.doi.org/10.1063/1.4805085 (9 pages)

Online Publication Date: 22 May 2013

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The two dissociative ionization channels of ethanol (C2H5OH) induced by an intense near-infrared laser pulse (λ ∼ 783 nm), C2H5OH → CH2OH+ + CH3 + e− and C2H5OH → C2H5+ + OH + e−, are investigated using photoelectron-photoion coincidence method. It is shown that both the electronic ground state and the first electronically excited state of C2H5OH+ are produced at the moment of photoelectron emission. From the observed correlation between the electronic states of C2H5OH+ prepared at the moment of photoelectron emission and the kinetic energy release of the fragment ions, it is revealed that C2H5OH+ prepared in the electronic ground state at the photoelectron emission gains larger internal energy in the end than that prepared in the electronically excited state. The averaged internal energy of C2H5OH+ just before the dissociation is found to increase when the laser field intensity increases from 9 to 23 TW/cm2 and when the laser pulse duration increases from 35 to 800 fs.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.60.+q Photoelectron spectra
33.70.Fd Absolute and relative line and band intensities
back to top Surfaces, Interfaces, and Materials

Thermionic current densities from first principles

Johannes Voss, Aleksandra Vojvodic, Sharon H. Chou, Roger T. Howe, Igor Bargatin, and Frank Abild-Pedersen

J. Chem. Phys. 138, 204701 (2013); http://dx.doi.org/10.1063/1.4805002 (5 pages)

Online Publication Date: 22 May 2013

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We present a density functional theory-based method for calculating thermionic emission currents from a cathode into vacuum using a non-equilibrium Green's function approach. It does not require semi-classical approximations or crude simplifications of the electronic structure used in previous methods and thus provides quantitative predictions of thermionic emission for adsorbate-coated surfaces. The obtained results match well with experimental measurements of temperature-dependent current densities. Our approach can thus enable computational design of composite electrode materials.
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79.40.+z Thermionic emission
68.43.Mn Adsorption kinetics

Ab initio and classical molecular dynamics studies of the structural and dynamical behavior of water near a hydrophobic graphene sheet

Malay Kumar Rana and Amalendu Chandra

J. Chem. Phys. 138, 204702 (2013); http://dx.doi.org/10.1063/1.4804300 (9 pages)

Online Publication Date: 22 May 2013

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The behavior of water near a graphene sheet is investigated by means of ab initio and classical molecular dynamics simulations. The wetting of the graphene sheet by ab initio water and the relation of such behavior to the strength of classical dispersion interaction between surface atoms and water are explored. The first principles simulations reveal a layered solvation structure around the graphene sheet with a significant water density in the interfacial region implying no drying or cavitation effect. It is found that the ab initio results of water density at interfaces can be reproduced reasonably well by classical simulations with a tuned dispersion potential between the surface and water molecules. Calculations of vibrational power spectrum from ab initio simulations reveal a shift of the intramolecular stretch modes to higher frequencies for interfacial water molecules when compared with those of the second solvation later or bulk-like water due to the presence of free OH modes near the graphene sheet. Also, a weakening of the water-water hydrogen bonds in the vicinity of the graphene surface is found in our ab initio simulations as reflected in the shift of intermolecular vibrational modes to lower frequencies for interfacial water molecules. The first principles calculations also reveal that the residence and orientational dynamics of interfacial water are somewhat slower than those of the second layer or bulk-like molecules. However, the lateral diffusion and hydrogen bond relaxation of interfacial water molecules are found to occur at a somewhat faster rate than that of the bulk-like water molecules. The classical molecular dynamics simulations with tuned Lennard-Jones surface-water interaction are found to produce dynamical results that are qualitatively similar to those of ab initio molecular dynamics simulations.
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61.20.Ja Computer simulation of liquid structure
68.08.Bc Wetting
66.10.C- Diffusion and thermal diffusion
82.30.Nr Association, addition, insertion, cluster formation
61.25.Em Molecular liquids

Dynamics of acetone photooxidation on TiO2(110): State-resolved measurements of methyl photoproducts

Matthew D. Kershis, Daniel P. Wilson, and Michael G. White

J. Chem. Phys. 138, 204703 (2013); http://dx.doi.org/10.1063/1.4805065 (7 pages)

Online Publication Date: 22 May 2013

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State-resolved laser techniques were used to study the internal state distributions of gas phase methyl radicals which are produced during the photooxidation of acetone on TiO2(110). This approach was used as a means of understanding the nature of the bimodal kinetic energy distributions for these radicals. Specifically, we investigated the population of the ν2 “umbrella mode” which has been shown to be important in similar photodissociation reactions where methyl radicals are liberated. We observed that for methyl radicals undergoing prompt dissociation (EK = 0.15 eV), the vibrational population in the umbrella mode is quite cold and can be characterized by a Tvib = 151 ± 15 K. Methyl radicals in this channel were also characterized by a rotational energy distribution of Trot = 325 ± 25 K which is comparable to the gas phase value obtained by acetone photolysis. State-resolved energy distributions also show that methyl radicals which are vibrationally excited have an overall kinetic energy distribution which is ∼35 meV less than those which are in their vibrational ground state. This value is comparable to, but not exactly in agreement with, the known vibrational spacing of the ν2 mode and suggests that vibrationally excited methyl radicals have less energy available for translation.
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82.50.Hp Processes caused by visible and UV light
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

On the thermoelectric transport properties of graphyne by the first-principles method

Xiao-Ming Wang, Dong-Chuan Mo, and Shu-Shen Lu

J. Chem. Phys. 138, 204704 (2013); http://dx.doi.org/10.1063/1.4806069 (8 pages)

Online Publication Date: 22 May 2013

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Graphyne, another two-dimensional carbon allotrope, has received increased attentions in recent years. By using the first-principles density functional calculations combined with the non-equilibrium Green's function formalism, we investigated the electronic, thermal, and thermoelectric transport properties of graphyne systematically and comparatively. It is found that the phonon thermal conductance of graphyne is greatly reduced compared to that of graphene in most temperature regions while larger than that of graphene at low temperatures, which is attributed to the different bond strengths and phonon spectra of graphyne and graphene. Due to the semiconductor property of graphyne, the thermoelectric power (TEP) is found to be one magnitude larger than that of graphene. Besides, distinct peak value regions of TEP in the contour of chemical potential and temperature are displayed for graphyne and graphene. Finally, the thermoelectric figure of merit (ZT) of graphyne is found to be much larger than that of graphene as a result of large TEP and greatly reduced thermal conductance in graphyne, which indicates preferred thermoelectric applications for graphyne.
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72.20.Pa Thermoelectric and thermomagnetic effects
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
72.80.Vp Electronic transport in graphene
73.22.Pr Electronic structure of graphene
65.80.Ck Thermal properties of graphene
71.20.Mq Elemental semiconductors

A microscopic picture of surface charge trapping in semiconductor nanocrystals

Jonathan Mooney, Michael M. Krause, Jonathan I. Saari, and Patanjali Kambhampati

J. Chem. Phys. 138, 204705 (2013); http://dx.doi.org/10.1063/1.4807054 (9 pages)

Online Publication Date: 22 May 2013

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Several different compositions of semiconductor nanocrystals are subjected to numerous spectroscopic techniques to elucidate the nature of surface trapping in these systems. We find a consistent temperature-dependent relationship between core and surface photoluminescence intensity and marked differences in electron-phonon coupling for core and surface states based on ultrafast measurements and Resonance Raman studies, respectively. These results support a minimal model of surface charge trapping applicable to a range of nanocrystal systems involving a single surface state in which the trapped charge polarization leads to strong phonon couplings, with transitions between the surface and band edge excitonic states being governed by semiclassical electron-transfer theory.
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78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Fs III-V and II-VI semiconductors
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
63.20.kd Phonon-electron interactions
back to top Polymers and Soft Matter
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An atomistic description of the nematic and smectic phases of 4-n-octyl-4′ cyanobiphenyl (8CB)

Mattia Felice Palermo, Antonio Pizzirusso, Luca Muccioli, and Claudio Zannoni

J. Chem. Phys. 138, 204901 (2013); http://dx.doi.org/10.1063/1.4804270 (16 pages)

Online Publication Date: 22 May 2013

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We report the results of atomistic molecular dynamics simulations of 4-n-octyl-4′ cyanobiphenyl (8CB) on samples of 750 and 3000 molecules showing the spontaneous formation of the nematic phase and then of smectic layers by gradually cooling down from the isotropic phase. Orientational, positional, and mixed order parameters, layer spacing, translational diffusion tensor components and their temperature dependence are reported. A detailed comparison with available experimental data validates the model and force field employed and clarifies the molecular organization of this important liquid crystal often used as reference smectic material.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
66.10.C- Diffusion and thermal diffusion
61.20.Ja Computer simulation of liquid structure
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Erratum: “Semilocal and hybrid density embedding calculations of ground-state charge-transfer complexes” [J. Chem. Phys. 138, 124112 (2013)]

S. Laricchia, E. Fabiano, and F. Della Sala

J. Chem. Phys. 138, 209901 (2013); http://dx.doi.org/10.1063/1.4807776 (1 page)

Online Publication Date: 22 May 2013

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Abstract Unavailable
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99.10.Cd Errata
31.15.eg Exchange-correlation functionals (in current density functional theory)
34.70.+e Charge transfer
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