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Journal of Physical Chemistry. A

Miroslava Trchova, Jaroslav Stejskal
Polypyrrole nanotubes rank among the most conducting forms of organic semiconductors. They are prepared by the oxidation of pyrrole in the presence of methyl orange. Other organic dyes, viz. ethyl orange, Acid Blue 25 and Acid Blue 125, have been used in the present study to prepare globules or nanofibers. The resulting polypyrroles were studied in detail by Raman spectroscopy. The apparent paradox when a dye contribution to spectra is absent with 785 nm excitation line and present with shorter wavelengths is explained by the resonance character of the Raman scattering which allows to separate the contributions from the polypyrrole surface and from the bulk...
November 12, 2018: Journal of Physical Chemistry. A
Shuyu Xu, Fernando P Sabino, Anderson Janotti, D Bruce Chase, Donald L Sparks, John F Rabolt
In this study, a 3D SERS substrate comprised of silver coated gold nanorods (Ag/AuNRs) decorated on electrospun polycaprolactone (PCL) fibers has been applied, for the first time, to quantitative analytical measurements on various arsenic species: p-arsanilic acid ( pAsA), roxarsone (Rox) and arsenate (AsV), with a demonstrated sensitivity below 5 ppb. AsV detection in a solution of common salt ions has been demonstrated, showing the tolerance of the substrate to more complex environments. pAsA adsorption behavior on the substrate surface has been investigated in detail using these unique SERS substrates...
November 12, 2018: Journal of Physical Chemistry. A
Brian D Adamson, Scott A Skeen, Musahid Ahmed, Nils Hansen
This paper provides experimental evidence for the chemical structures of aliphatically substituted and aliphatically bridged polycyclic aromatic hydrocarbon (PAH) species in the gas-phase of combustion environments. The identification of these single- and multi-core aromatic species, which have been hypothesized to be important in PAH growth and soot nucleation, was made possible through a combination of sampling gaseous constituents from an atmospheric pressure inverse co-flow diffusion flame of ethylene and high-resolution tandem mass spectrometry (MS-MS)...
November 12, 2018: Journal of Physical Chemistry. A
Shubhra Sarkar, N Ramanathan, K Sundararajan
The simultaneous possession of π-electron clouds and acidic hydrogen atoms in pyrrole (C4 H5 N) and phenol (C6 H5 OH) framework opens the potentiality in exploring the synergistic interactions in their weakly bonded complexes. In this work, the synergistic hydrogen bonding in C4 H5 N-C6 H5 OH complexes is therefore investigated using FTIR spectroscopy under isolated conditions at low temperatures. Computations performed at DFT, DFT-GD3, M06, and MP2 level of theories employing aug-cc-pVDZ basis set yielded three minima on the potential energy surface for the 1:1 complex of C4 H5 N-C6 H5 OH...
November 12, 2018: Journal of Physical Chemistry. A
Kamal Sharkas, Lin Li, Kai Trepte, Kushantha P K Withanage, Rajendra P Joshi, Rajendra R Zope, Tunna Baruah, J Karl Johnson, Koblar Alan Jackson, Juan E Peralta
The self-interaction error (SIE) is one of the major drawbacks of practical exchange-correlation functionals for Kohn-Sham density functional theory. Despite this, the use of methods that explicitly remove SIE from approximate density functionals is scarce in the literature due to their relatively high computational cost and lack of consistent improvement over standard modern functionals. In this article we assess the performance of a novel approach recently proposed by Pederson, Ruzsinszky, and Perdew [J. Chem...
November 9, 2018: Journal of Physical Chemistry. A
Soonho Kwon, Saber Naserifar, Hyuck Mo Lee, William A Goddard
The Polarizable Charge Equilibration (PQEq) method was developed to provide a simple but accurate description for the electrostatic interactions and polarization effects in materials. Previously, we optimized the 4 parameters per element for the main group elements1, 2. Here, we extend this optimization to the 24 d-block transition-metal (TM) elements, column 4 to 11 of the periodic table including Ti-Cu, Zr-Ag, and Hf-Au. We validate the PQEq description for these elements by comparing to interaction energies computed by quantum mechanics (QM)...
November 9, 2018: Journal of Physical Chemistry. A
Quinton J Meisner, Ali Haidar Younes, Zhao Yuan, Kesavapillai Sreenath, Joseph J M Hurley, Lei Zhu
Excitation-dependent multiple fluorescence of a 2-(2'-hydroxyphenyl)benzoxazole (HBO) derivative (1) is described. Compound 1 contains the structure of a charge transfer (CT) 4-hydroxyphenylvinylenebipy fluorophore and an excited state intramolecular proton transfer (ESIPT)-capable HBO component that intersect at the hydroxyphenyl moiety. Therefore, both CT and ESIPT pathways, while spatially mostly separated, are available to the excited state of 1. The ESIPT process offers two emissive isomeric structures (enol and keto) of 1 in the excited state, while the susceptibility of 1 to a base adds another option to tune the composite emission color...
November 9, 2018: Journal of Physical Chemistry. A
M F Francis
No abstract text is available yet for this article.
November 9, 2018: Journal of Physical Chemistry. A
Dumitru Sirbu, Joshua K G Karlsson, Anthony Harriman
A boron dipyrromethene (BODIPY) derivative has been synthesized whereby a phenoxyl ring attached at the 3-position is bound through the oxygen atom to the boron center. This compound is structurally distorted, with the molecular surface being curved, and undergoes further geometrical perturbation at the excited-singlet state level. Fluorescence is readily observed in solution at ambient temperature, with the quantum yield rising with increasing viscosity of the surrounding solvent. Dual-exponential decay kinetics are observed, corresponding to E-type delayed fluorescence...
November 9, 2018: Journal of Physical Chemistry. A
Jie Hu, Chun-Xiao Wu, Yunsheng Ma, Shan Xi Tian
High-lying quantum states of molecule are apt to be populated by translational-to-internal energy transfer in the collisions with atom, which usually becomes more significant with the increase of collision energy. However, in the charge exchange reaction Ar+ + NO → Ar + NO+ , the products NO+ prefer a dominant population at the lowest triplet state a3 Σ+ , in particular, in the higher energy collisions; the higher states b3 Π and w3 Δ of NO+ are accessed only at the lower collision energies. Such a striking collision-energy dependence is attributed to two distinctly different processes: the former is controlled with an energetically resonant charge-transfer mechanism; while the latter experiences an intermediate complex (Ar-NO)+ which permits a more efficient translational-to-internal energy transfer...
November 9, 2018: Journal of Physical Chemistry. A
Jenny W Fothergill, Andres C Hernandez, William B Knowlton, Bernard Yurke, Lan Li
The excited state properties of cyanine dyes and the orientations of their aggregates were studied using density functional theory (DFT). The effects of exchange-correlation functional and solvent model on the absorption spectrum of Cy5 was investigated. Using the 6-31+G(d,p) basis set and B3LYP exchange-correlation functional with IEF-PCM (water) solvent, the predicted spectrum achieved a maximum absorbance within 0.007 eV of experiment. An in-house program based on the theoretical model of Kühn, Renger, and May (KRM), which predicts the orientation of dyes within an aggregate from its absorbance and circular dichroism (CD) spectra or vice versa, was used to investigate the orientation of an experimentally observed dimer...
November 9, 2018: Journal of Physical Chemistry. A
Rosario C Sausa, Iskander G Batyrev, Rose A Pesce-Rodriguez, Edward F C Byrd
Density function theory (DFT) and experimental characterization of energetic materials play important roles in understanding molecular structure-property relations and validating models for their predictive capabilities. Here, we report our modeling and experimental results on the molecular, vibrational, and crystal structure of energetic bis-oxadiazole-bis-methylene dinitrate (BODN) obtained by molecular DFT (M-DFT) at the B3LYP- 6-31G** level, crystal DFT (C-DFT) using the Perdew-Burke-Ernzerhof functional optimized with norm-conserving pseudopotentials, X-ray diffractometry, infrared and Raman spectroscopy, and thermogravimetric analysis...
November 9, 2018: Journal of Physical Chemistry. A
Michael Lucas, Stephen J Brotton, Shashi Kant Shukla, Jiang Yu, Scott L Anderson, Ralf I Kaiser
Understanding the reaction mechanisms of ionic liquids and their oxidizers is necessary to develop the next generation of hypergolic, ionic-liquid-based fuels. We studied reactions between a levitated droplet of 1-allyl-3-methylimidazolium dicyanamide ([AMIM][DCA]), with and without hydrogen-capped boron nanoparticles, and nitrogen dioxide (NO2 ). The reactions were monitored with Fourier-transform infrared (FTIR) and Raman spectroscopy. The emergence of new structures in the FTIR and Raman spectra is consistent with the formation of functional groups including organic nitrites (RONO), nitroamines (R1 R2 NNO2 ), and carbonitrates (R1 R2 C=NO2 - )...
November 9, 2018: Journal of Physical Chemistry. A
Laura A Mertens, Iftikhar A Awan, David Allan Sheen, Jeffrey A Manion
Evaluated site-specific rate constants for the reactions of isobutane with CH3 and H were determined in a combined analysis of new shock tube experiments and existing literature data. In our shock tube experiments, CH3 radicals, produced from the pyrolysis of di- tert-butylperoxide, and H atoms, produced from the pyrolysis of C2 H5 I, were reacted with dilute mixtures of isobutane in argon at 870 K to 1130 K and 140 kPa to 360 kPa, usually with a radical chain inhibitor. Propene and isobutene, measured with GC/FID and MS, were quantified as characteristic of H-abstraction from the primary and tertiary carbons, respectively...
November 8, 2018: Journal of Physical Chemistry. A
Guanghua Ren, Qingchi Meng, Jinfeng Zhao, Tianshu Chu
Proton-coupled electron transfer (PCET) reactions play important roles in solar energy conversion processes. Designing efficient artificial photosystems with PCET mechanisms is a promising solution for the growing demands of energy resources. Compared to ground states, inducing the PCET reactions directly from electronically excited states, named excited-state PCET (ES-PCET) reactions, is a more direct and efficient avenue to the formation of solar fuels. Here, based on benzimidazole phenolic derivatives, we have designed and studied some molecular structures that can undergo the electron-driven double-proton transfer (EDDPT) reactions within the ES-PCET framework...
November 8, 2018: Journal of Physical Chemistry. A
Soren K Mellerup, Goonay Yousefalizadeh, Suning Wang, Kevin G Stamplecoskie
N,C-chelate organoborates represent an emerging class of photoresponsive materials due to their photochromic switching at a boron center. Despite the promising applicability of such systems, little is known about the excited-state processes that lead to their unique photoreactivity, which is detrimental to the design of next-generation smart materials based on boron. As part of our ongoing effort to understand and improve the utility of these organoboron compounds, we report some of the first experimental evidence to support an excited-state mechanism for N,C-chelate organoborates...
November 8, 2018: Journal of Physical Chemistry. A
Sharon Priya Gnanasekar, Elangannan Arunan
Atoms in Molecules (AIM), Natural Bond Orbital (NBO), and normal coordinate analysis have been carried out at the global minimum structures of TH5+ (T = C/Si/Ge). All these analyses lead to a consistent structure for these three protonated TH4 molecules. The CH5+ has a structure with three short and two long C-H covalent bonds and no H-H bond. Hence, the popular characterization of protonated methane as a weakly bound CH3+ and H2 is inconsistent with these results. However, SiH5+ and GeH5+ are both indeed a complex formed between TH3+ and H2 stabilized by a tetrel bond, with the H2 being the tetrel bond acceptor...
November 8, 2018: Journal of Physical Chemistry. A
Samuel M Hickenlooper, Conner C Harper, Brigham L Pope, Daniel N Mortensen, David V Dearden
Factors affecting the extrusion of guests from metal ion capped decamethylcucurbit[5]uril (mc5) molecular cage complexes are investigated using both collision-induced dissociation techniques and molecular mechanics simulations. For guests without polar bonds, the extrusion barrier increases with increasing guest volume. This is likely because escape of larger guests requires more displacement of the metal ion caps and, thus, more disruption of the ion-dipole interactions between the ion caps and the electronegative rim oxygens of mc5 to occur...
November 8, 2018: Journal of Physical Chemistry. A
Tarek Trabelsi, K Mahjoubi, B Mehnen, Majdi Hochlaf, Joseph S Francisco
Standard and explicitly correlated coupled cluster theory computations in conjunction with large basis sets are performed to characterize the [Al,P,O] isomers. Three isomers, namely linear-AlOP, bent-AlOP and linear-OAlP, are found as stable species. Their optimized equilibrium geometries, harmonic vibrational frequencies, rotational constants and relative energies are deduced. In addition, a set of spectroscopic parameters is generated from the three-dimensional potential energy surfaces (3D-PESs) of each isomer at the (R)CCSD(T)/aug-cc-pV5Z level...
November 8, 2018: Journal of Physical Chemistry. A
Marco Fioroni, A Kelly Tartera, Nathan J DeYonker
The formation of the chiral molecule propylene oxide (CH3 CHCH2 O) recently detected in the interstellar medium (ISM) is proposed to take place on an amorphous silicate grain surface where peroxo defects are present. A computational analysis conducted at the DFT and MP2-F12 levels of theory on a neat amorphous silica model supports such a hypothesis resulting in (a) strong thermodynamic driving forces and low activation energies allowing the synthesis of CH3 CHCH2 O at low temperatures, (b) chemical defects on silica surfaces promoting heterogeneous catalysis of the increasing molecular complexity found in interstellar and circumstellar medium, and (c) chemical defects that have implications on understanding how processing phases modify the nature of the reactive groups on a silica surface affecting the surface catalytic activity...
November 8, 2018: Journal of Physical Chemistry. A
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