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Journal of Physical Chemistry. A

Corrine A Kumar, Arjun Saha, Krishnan Raghavachari
Transition metal sulfides (TMS) are being investigated with increased frequency because of their ability to efficiently catalyze the hydrogen evolution reaction. We have studied the trimetallic TMS cluster ions, Mo3S4(-), W3S4(-), and W3S3(-), and probed their efficiency for bond activation and hydrogen evolution from water. These clusters have geometries that are related to the edge sites on bulk MoS2 surfaces that are known to play a role in hydrogen evolution. Using density functional theory, the electronic structures of these clusters and their chemical reactivity with water have been investigated...
February 17, 2017: Journal of Physical Chemistry. A
Kasper Planeta Kepp
Gold plays a major role in nanochemistry, catalysis, and electrochemistry. Accordingly, hundreds of studies apply density functionals to study chemical bonding with gold, yet there is no systematic attempt to assess the accuracy of these methods applied to gold. This paper reports a benchmark against 51 experimental bond enthalpies of AuX systems and seven additional polyatomic and cationic molecules. 12 density functionals were tested, covering meta functionals, hybrids with variable HF exchange, double-hybrid, dispersion-corrected and non-hybrid GGA functionals...
February 17, 2017: Journal of Physical Chemistry. A
Colleen Bertoni, Lyudmila V Slipchenko, Alston J Misquitta, Mark S Gordon
In the effective fragment potential (EFP) method the Coulomb potential is represented using a set of multipole moments generated by the distributed multipole analysis (DMA) method. Misquitta, Stone, and Fazeli recently developed a basis space-iterated stockholder atom (BS-ISA) method to generate multipole moments. This study assesses the accuracy of the EFP interaction energies using sets of multipole moments generated from the BS-ISA method, and from several versions of the DMA method (such as analytic and numeric grid-based), with varying basis sets...
February 17, 2017: Journal of Physical Chemistry. A
Le Nhan Pham, Minh Tho Nguyen
Electronic structures of both the anionic and neutral triatomic species TiGe2-/0 were theoretically studied employing single-reference (DFT and RCCSD(T)) and multiconfigurational (CASSCF/CASPT2 and CASSCF/NEVPT2) methods with large basis sets. The ground state of TiGe2- (C2v) was identified to be 4B1 but the 2A1 state is nearly degenerate, whereas the 3B1 is clearly the ground state of the neutral TiGe2 (C2v). On the basis of the computed ground and excited states of both neutral and anionic structures, all electronic transitions giving rise to experimental anion photoelectron bands in the spectrum of TiGe2- can now be assigned...
February 17, 2017: Journal of Physical Chemistry. A
Bridget Salna, Abdelkrim Benabbas, Paul M Champion
The often-used "linear approximation" for treating the coupling of donor-acceptor (D-A) distance fluctuations to proton-coupled electron transfer tunneling reactions, is systematically examined. The accuracy of this approximation is found to depend upon the potential energy surfaces that are used to describe both the tunneling particle vibrations and the D-A coordinate probability distribution. A harmonic treatment of both the tunneling particle and the D-A coordinates results in a significant breakdown of the linear approximation when the width of the D-A distribution exceeds ~0...
February 17, 2017: Journal of Physical Chemistry. A
Takuya Okamura, Nobuyuki Akai, Munetaka Nakata
Reaction mechanisms of nitrene, one of the most famous biradicals, have been frequently studied, and many spectral data have been obtained so far. In the present study, the experimental IR spectra of triplet 8-amino-1-naphthylnitrene ((3)ANN), a triplet diimine biradical 1,8-dihydro-1,8-naphthalenediimine ((3)DND), and 1,2-dihydrobenz[cd]indazole (DBI), which are produced in the UV photolysis of 1,8-diaminonaphthalene in an Ar matrix and identified by a combination method of IR spectroscopy and DFT quantum chemical calculations, are first reported...
February 17, 2017: Journal of Physical Chemistry. A
Stuart Carter, Yimin Wang, Joel M Bowman
The code MULTIMODE is used in its reaction path version, along with ab initio potential energy and dipole moment surfaces introduced earlier, to predict the infrared spectra of both trans and cis forms of HOCO at temperatures 296 and 15 K. All six fundamentals are isolated for each isomer and temperature, and their main features examined, paying particular attention to the OH stretch fundamental, whose spectrum has been reported experimentally for trans-HOCO. The current spectra for cis-HOCO, while not of "spectroscopic" accuracy, should be sufficient to aid in new experimental efforts to record the spectrum of this isomer...
February 17, 2017: Journal of Physical Chemistry. A
L Orian, R Pilot, R Bozio
The static electric polarizabilities (α) of a quadrupolar squaraine dye are investigated in silico, either as the excess polarizability, i.e., the change from the ground to the lowest excited state, Δα, or as those of the two states separately, depending on the approach. The polarizabilities are worked out by making use of the energy and dipole moment Taylor expansions as a function of the electric field (E), in which α is represented by the quadratic and linear terms, respectively, and also by means of the linear response approach...
February 17, 2017: Journal of Physical Chemistry. A
Lais N Magno, Fabio C Bezerra, Luiz E S Freire, Rubens A Guerra, Andris Figueiroa Bakuzis, Pablo Jose Goncalves
Modern medicine has been searching for new and more efficient strategies for diagnostics and therapeutics applications. Considering this, porphyrin molecules have received great interest for applications in photodiagnostics and phototherapies, even as magnetic nanoparticles for drug-delivery systems and magnetic-hyperthermia therapy. Aiming to obtain a multifunctional system, which combines diagnostics with therapeutic functions on the same platform, the present study employed UV/Vis absorption and fluorescence spectroscopies to evaluated the interaction between meso-tetrakis(p-sulfonatofenyl) porphyrin (TPPS) and maghemite nanoparticles (γ-Fe2O3)...
February 16, 2017: Journal of Physical Chemistry. A
Daigo Masuzaki, Toshiaki Nagata, Fumitaka Mafune
Thermal dissociation of cationic niobium oxide clusters (NbnOm+) was investigated by gas phase thermal desorption spectrometry. The dominant species formed at 300 K were NbnO2.5n+p (n = 2, 4, 6, …; p = 0, 1, 2, …) and NbnO2.5n-0.5+q (n = 3, 5,…; q = 0, 1, 2, …). At higher temperatures, the more oxygen-rich clusters were observed to release O2. However, the desorption of O2 from NbnOm+ was found to be insignificant in comparison with VnOm+ because Nb tends to have a +5 oxidation state exclusively, whereas V can have both +4 and +5 oxidation states...
February 16, 2017: Journal of Physical Chemistry. A
Stefania Cagnina, Andre Nicolle, Theodorus De Bruin, Yuri Georgievskii, Stephen J Klippenstein
The design of innovative combustion processes relies on a comprehensive understanding of biodiesel oxidation kinetics. The present study aims at unraveling the reaction mechanism involved in the epoxidation of a realistic biodiesel surrogate, methyl trans-3-hexenoate, by hydroperoxy radicals using a bottom-up theoretical kinetics methodology. The obtained rate constants are in good agreement with experimental data for alkenes epoxidation by HO2. The impact of temperature and pressure on epoxidation pathways involving H-bonded and non H-bonded conformers was assessed...
February 16, 2017: Journal of Physical Chemistry. A
Mark W Kelly, Sarah C Halliwell, W Jeff Rodgers, Jason D Pattle, Jeremy N Harvey, Michael N R Ashfold
Quantum mechanical and hybrid quantum mechanical/molecular mechanical (QM/MM) cluster models have been used to investigate possible reaction mechanisms whereby gas phase NHx (x = 0-2), CNHx (x = 0, 1) and OH radicals can add to, and incorporate in, a C-C dimer bond on the C(100):H 21 diamond surface during chemical vapor deposition from microwave activated C/H containing gas mixtures containing trace amounts of added N or O. Three N incorporation routes are identified, initiated by N, NH and CN(H) addition to a surface radical site, whereas only OH addition was considered as the precursor to O incorporation...
February 16, 2017: Journal of Physical Chemistry. A
Kevin M Hickson, Yury V Suleimanov
In the present joint experimental and theoretical study, we report thermal rate constants for the O(1D) + H2 reaction within the 50-300 K temperature range. Experimental kinetics measurements were performed using a continuous supersonic flow reactor coupled with pulsed laser photolysis for O(1D) production and pulsed laser induced fluorescence in the vacuum ultraviolet wavelength range (VUV LIF) for O(1D) detection. Theoretical rate constants were obtained using the ring polymer molecular dynamics (RPMD) approach over the two lowest potential energy surfaces 11A and 11A which possess barrierless and thermally activated energy profiles, respectively...
February 16, 2017: Journal of Physical Chemistry. A
David B Lingerfelt, Patrick J Lestrange, Joseph J Radler, Samantha E Brown-Xu, Pyosang Kim, Felix N Castellano, Lin X Chen, Xiaosong Li
Materials and molecular systems exhibiting long-lived electronic coherence can facilitate coherent transport, opening the door to efficient charge and energy transport beyond traditional methods. Recently, signatures of a possible coherent, recurrent electronic motion were identified in femtosecond pump-probe spectroscopy experiments on a bi-nuclear platinum complex, where a persistent periodic beating in the transient absorption signal's anisotropy was observed. In this study, we investigate the excitonic dynamics that underlie the suspected electronic coherence for a series of bi-nuclear platinum complexes exhibiting a range of inter-platinum distances...
February 16, 2017: Journal of Physical Chemistry. A
Alberto P Munuzuri, Juan Pérez-Mercader
Synchronization of intercommunicating individual oscillators is an important form of collective behavior used in Nature as a mechanism to face dangers, act collectively and communicate. The involvement of the medium where oscillators exist is an important ingredient. Because of their nature and/or their multiple different components the medium and the environment are often perceived as stochastic relative to the deterministic nature of the individuals at some scale. This injects energy/matter into the system in ways that can enhance or deenhance communication in a stochastic manner...
February 16, 2017: Journal of Physical Chemistry. A
Mohammad Alaghemandi, Lucas B Newcomb, Jason R Green
Hydrogen is a potential substitute for fossil fuels that would reduce the combustive emission of carbon dioxide. However, the low ignition energy needed to initiate oxidation imposes constraints on the efficiency and safety of hydrogen-based technologies. Microscopic details of the combustion processes, ephemeral transient species, and complex reaction networks are necessary to control and optimize the use of hydrogen as a commercial fuel. Here, we report estimates of the ignition time of hydrogen-oxygen mixtures over a wide range of equivalence ratios from extensive reactive molecular dynamics simulations...
February 16, 2017: Journal of Physical Chemistry. A
Malte Döntgen, Kai Leonhard
Chemical activation of intermediates, such as hydrogen abstraction products, is emerging as a basis for a fully new reaction type: hot β-scission. While for thermally equilibrated intermediates chemical kinetics are typically orders of magnitude slower than relaxational kinetics, chemically activated intermediates raise the issue of inseparable chemical and relaxational kinetics. Here, this separation problem is discussed in the framework of master equation simulations, proposing three cases often encountered in chemistry: insignificant chemical activation, predominant chemical activation, and the transition between these two limits...
February 16, 2017: Journal of Physical Chemistry. A
Yuri Bedjanian, Julien Morin
Reaction of oxygen atoms with propene is an important step in combustion processes particularly affecting the profiles of intermediate species and flame speed. The relative importance of different pathways of this multichannel reaction at different temperatures represents significant theoretical interest and is essential for modeling combustion systems. In the present work, we report the first experimental investigation of the products of the O((3)P) + C3H6 reaction over an extended temperature range (298-905 K)...
February 16, 2017: Journal of Physical Chemistry. A
Kiet A Nguyen, Ruth Pachter, Paul N Day
We present calculated one- and two-photon absorption (OPA, TPA) spectra for molecular neutral, cation, and anion cadmium chalcogenide nonstoichiometric clusters [CdnE'm'(ER)m, E = S and Se, R = hydrogen, methyl, phenyl, para-nitrophenyl, para-cyanophenyl], ranging from less than 1 nm to more than 2 nm in size with well-defined structures. A systematic treatment of the clusters is carried out to assess the effects of size and ligand on their linear and nonlinear optical properties. Ligands and cluster size were found to have a large influence on the color and intensity of the electronic absorption spectra...
February 16, 2017: Journal of Physical Chemistry. A
Yukio Kawashima, Kimihiko Hirao
We introduced two methods to correct the singularity in the calculation of long-range HF exchange for long-range corrected density functional theory (LC-DFT) calculations in plane-wave basis sets. The first method introduces an auxiliary function to cancel out the singularity. The second method introduces a truncated long-range Coulomb potential, which has no singularity. We assessed the introduced methods using the LC-BLYP functional by applying it to isolated systems of naphthalene and pyridine. We first compared the total energies and the HOMO energies of the singularity-corrected and uncorrected calculations and confirmed that singularity correction is essential for LC-DFT calculations using plane-wave basis sets...
February 15, 2017: Journal of Physical Chemistry. A
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