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Journal of Physical Chemistry. A

Dmitry A Telnov, Dmitry A Krapivin, John Thomas Heslar, Shih-I Chu
We perform a theoretical and computational study of relativistic one-electron homonuclear diatomic quasimolecules subject to strong electromagnetic fields linearly polarized along the molecular axis. Several quasimolecules with the nuclear charges 1 to 92 and appropriately scaled internuclear distances and field parameters are used in the calculations. The time-dependent Dirac equation is solved with the help of the generalized pseudospectral method in prolate spheroidal coordinates. We have found that employing this coordinate system makes it possible to avoid emergence of spurious states, which usually show up when solving the Dirac equation numerically...
September 17, 2018: Journal of Physical Chemistry. A
Tyler Nelson, Anita L Cochran, Colin M Western
We modeled observations of the C2 d3 Πg - a3 Πu (Swan) Δν = 0 sequence observed in spectra of comet 122P/de Vico obtained with the 2.7m Harlan J. Smith Telescope and Tull Coude spectrograph of McDonald observatory on 10/03/1995 and 10/04/1995 . The data used spanned 4986-5169Å at R=λ/Δλ=60,000. We used the PGOPHER molecular spectra model to generate and fit synthetic spectra with the d3 Πg having one and two rotational temperatures. We found the excited state had a two component rotational temperature, similar to that found for comet Halley...
September 17, 2018: Journal of Physical Chemistry. A
Sharmistha Urinda, Goutam Das, Anup Pramanik, Pranab Sarkar
Tuning photoluminescence properties is of prime importance for designing efficient light emitting diode (LED) materials. Here, we perform a computational study on the effect of normal N-heterocyclic carbene (NHC) and abnormal mesoionic carbene (MIC) ligands on the photoluminescence properties of some Ir(III) complexes, which are very promising LED materials. We find MIC as the privileged ligand in designing triplet emitters. The strong σ-donating and moderate π-accepting properties of MIC render a lower access to the nonemissive triplet metal-centered state (3 MC), resulting in lowering the nonradiative rate constant ( knr ) and correspondingly achieving higher quantum efficiency...
September 17, 2018: Journal of Physical Chemistry. A
Mckay Whetton Easton, John Joseph Nash, Hilkka I Kenttamaa
A full understanding of all possible elementary reactions applicable to cellulose fast pyrolysis is key to developing a comprehensive kinetic model for fast pyrolysis of cellulose. Since water is an observed product of fast pyrolysis of cellulose, the energetics of the dehydration reactions of cellulose were explored computationally by using density functional theory (DFT). Glucose and cellobiose were selected as the cellulose model compounds. The four water loss mechanisms studied are: Maccoll elimination, Pinacol ring contraction, cyclic Grob fragmentation, and alcohol condensation, some of which have not been considered previously in the literature...
September 14, 2018: Journal of Physical Chemistry. A
Kathleen L Sampson, Xiaoqin Jiang, Esmeralda Bukuroshi, Aleksa Dovijarski, Hasan Raboui, Timothy P Bender, Karl M Kadish
No abstract text is available yet for this article.
September 14, 2018: Journal of Physical Chemistry. A
Xuhui Lin, Wei Wu, Kenneth B Wiberg, Yirong Mo
Most recently, Wiberg and Rablen examined a few substituted methanes and identified the polar effect, which is associated with the atomic charge at the central carbon, as a possible factor for bond energy changes while the exact role of the hyperconjugation effect is unsettled. In this work, we revisited a series of substituted methanes CH4- n X n ( n = 0-4, X= F, Cl, CN, OCH3 ) by explicitly computing the intramolecular electron delocalization energies using the simplest variant of ab initio valence bond (VB) theory, namely the block-localized wave function (BLW) method...
September 14, 2018: Journal of Physical Chemistry. A
Rui Wei, Xiuting Chen, Yu Gong
Sulfonyl fluoride anion (SO2 F2 - ) was produced during codeposition of laser-ablated metal atoms, ions, and electrons with SO2 F2 in argon and neon matrixes at 4 K. The structure of SO2 F2 - was determined by infrared spectroscopy and density functional theory calculations. On the basis of the experiments using 34 SO2 F2 and S18 O2 F2 samples, the three absorptions at 1284.9, 1109.3, and 567.0 cm-1 in argon and 1289.0, 1116.2, and 576.8 cm-1 in neon were assigned to the antisymmetric and symmetric O-S-O stretching and SO2 wagging modes of SO2 F2 - , respectively...
September 14, 2018: Journal of Physical Chemistry. A
Christina H McCulley, Dean J Tantillo
The results of quantum chemical calculations on putative biosynthetic carbocation cyclization/rearrangements leading to pupukeanane and related sesquiterpenes indicate that a secondary carbocation proposed as an intermediate is not a minimum on the potential energy surface and instead resides in a region of the potential energy surface associated with a plateau containing multiple exit channels.
September 13, 2018: Journal of Physical Chemistry. A
Steffen Spieler, Chinh H Duong, Alexander Kaiser, Felix Dünsing, Katharina Geistlinger, Moritz Fischer, Nan Yang, S Sunil Kumar, Mark A Johnson, Roland Wester
Vibrational spectra of protonated tryptophan and microsolvated TrpH+(H2O)m=1,2 were recorded by predissociation of H2 messenger tags using cryogenic ion traps. We explore the issue of messenger induced spectral changes by solvating TrpH+(H2)n with n=1-5 to obtain single photon vibrational spectra of TrpH+ and of its partly deuterated isotopomer in the spectral region of 800-4400 cm-1. Depending on the number of messenger molecules, the spectra of several conformational isomers associated with multiple H2 binding locations along with two natural conformations of TrpH+ were found using the two photon MS3IR2 conformational hole burning method...
September 13, 2018: Journal of Physical Chemistry. A
Yan Wang, Pengfei Liu, Yong Jie Li, Adam P Bateman, Scot T Martin, Hui-Ming Hung
The atmospheric reactions of secondary organic material (SOM) with gaseous reactants alter its composition and properties, which can further impact the Earth system. To investigate how water content and precursor affect the reactivity of SOM, the reaction between toluene-derived SOM and ammonia for variable relative humidity (RH) was investigated. A Fourier transform infrared spectrometer was used to monitor the absorbance change of the functional groups as a function of exposure time. There was a fast response to water vapor compared with a gradual spectral variation associated with ammonia uptake...
September 13, 2018: Journal of Physical Chemistry. A
Thanh Lam Nguyen, John F Stanton
The master equation technique is a standard tool to interpret gas-phase experimental kinetic results as well as to provide phenomenological rate coefficients for modeling. When there are significant changes of rotational constants along the reaction coordinate from a reactant through a transition state (TS) to product(s), including effects of angular momentum explicitly in a master equation model becomes vitally important. In this work, assuming that the K quantum number is adiabatic for both the TS and reactant, we developed an algorithm for pragmatic solutions of a three-dimensional master equation (3DME) that involves internal energy, total angular momentum ( J), and its projection K...
September 13, 2018: Journal of Physical Chemistry. A
Jonathan Ryan Hunt, Jahan M Dawlaty
Control of proton transfer is relevant to many areas in chemistry, particularly in catalysis where the kinetics of (de)protonation reactions are often rate limiting. Photobases, which are molecules with enhanced basicity in the excited state, allow for control of proton transfer with light and have the potential to be used as functional units in catalytic systems. Alcohols are the feedstock in many catalytic reactions, where their deprotonation or dehydrogenation is often important. We report that the photobase 5-methoxyquinoline can deprotonate a series of alcohols upon excitation by light...
September 12, 2018: Journal of Physical Chemistry. A
Kaiqiang Zhang, Stefan T Thynell
A detailed mechanism has been developed for thermal decomposition of HAN solutions, based on quantum mechanical calculations using the SMD-ωB97X-D method. The mechanism describes multiple kinetic processes, including nitration and nitrosation of hydroxylamine, HNO dimerization, and HONO-regeneration pathways involving H-abstraction reactions. Rate constants of elementary reactions were estimated using transition state theory with consideration of species' diffusion effect. Kinetic modeling was performed to predict species' evolutions in 0...
September 12, 2018: Journal of Physical Chemistry. A
Vincent Tognetti, Arnaldo F Silva, Mark A Vincent, Laurent Joubert, Paul L A Popelier
We discuss two main approaches to decompose the Møller-Plesset perturbation theory molecular energies into atomic contributions within the interacting quantum atoms (IQA) formalism, as implemented in the programs Morphy and AIMAll. For this purpose, the so-called intraatomic energies (also known as self-energies) of a representative set of 55 small molecules are compared with each other. The origin of the possible discrepancies between both approaches is analyzed, and linear models linking the two approaches are proposed for each atom type...
September 12, 2018: Journal of Physical Chemistry. A
Nureshan Dias, Baptiste Joalland, Nuwandi M Ariyasingha, Arthur G Suits, Bernadette M Broderick
The UV photodissociation of isoxazole (c-C3 H3 NO) is studied in this work by chirped-pulse Fourier transform mm-wave spectroscopy in a pulsed uniform Laval flow. This approach offers a number of advantages over traditional spectroscopic detection methods due to its broadband, sub-MHz resolution, and fast-acquisition capabilities. In coupling this technique with a quasi-uniform Laval flow, we are able to obtain product branching fractions in the 193 nm photodissociation of isoxazole. Five dissociation channels are explored through direct detection of seven different photoproducts...
September 12, 2018: Journal of Physical Chemistry. A
Wenhao Sun, Jennifer van Wijngaarden
Two new NCS-containing carbon chains of potential astronomical interest, HC4 NCS and NC3 NCS, were produced through dc electric discharge in a molecular beam and detected by Fourier transform microwave spectroscopy. Rotational transitions from the two species were recorded between 4 and 26 GHz, and assignments were confirmed by the distinct hyperfine structures due to the 14 N nuclear quadrupole moments of these two linear, isoelectronic species. The rotational constants of HC4 NCS and NC3 NCS were determined experimentally to be 595...
September 12, 2018: Journal of Physical Chemistry. A
Sebastian Peukert, Paul Sela, Damien Nativel, Jürgen Herzler, Mustapha Fikri, Christof Schulz
Shock-tube experiments have been performed to investigate the thermal decomposition of the oxygenated hydrocarbon dimethoxymethane (DMM; CH3 OCH2 OCH3 ). The primary initial reaction channels of DMM decomposition are considered to be the two bond fissions: CH3 OCH2 OCH3 → CH3 O + CH2 OCH3 (1) and CH3 OCH2 OCH3 → CH3 + OCH2 OCH3 (2). In the present work, two shock-tube facilities and three different detection techniques have been combined: Behind reflected shock waves, we have carried out time-resolved measurements of (i) the formation of H atoms using the highly sensitive H-ARAS (Atomic Resonance Absorption Spectrometry) technique and (ii) the depletion of the DMM reactant by high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS)...
September 12, 2018: Journal of Physical Chemistry. A
Luigi Gentile, Tao Wang, Anders Tunlid, Ulf Olsson, Per Persson
Ferrihydrite (Fh) nanoparticles are omnipresent in nature and often highly mobile because of their colloidal stability. Thus, Fh serves as a vector for iron as well as associated nutrients and contaminants. Here, we demonstrate, using small-angle X-ray scattering combined with cryo-transmission electron microscopy (cryo-TEM), that dissolved organic matter (DOM), extracted from a boreal forest soil, induce aggregation of Fh nanoparticles, of radius 3 nm, into fractal aggregates, having a fractal dimension D = 1...
September 12, 2018: Journal of Physical Chemistry. A
Dandan Ma, Xuefen Tian, Lifen Guo, Jie Mou, Sen Lin, Jianyi Ma
Many mode-specific behaviors in the gas phase and at the gas-surface interface have been reported in the past decades. Infrared activation of a reagent vibrational mode is often used to study these reactions. In this work, an inexpensive and easily applied scheme using microwave irradiation is proposed for activating complex-forming reactions by transferring populations between closely spaced resonances. The important combustion reaction of H + O2 ↔ O + OH is used as a model system to demonstrate the feasibility of the proposed approach...
September 12, 2018: Journal of Physical Chemistry. A
Maria Harris Rasmussen, Andreas Lynge Vishart, Freja E Storm, Kurt V Mikkelsen
Twelve dyad structures were investigated using time-dependent density functional theory (TD-DFT). The dyads are all functionalized boron subphthalocyanines (SubPcs), where the SubPc unit acts as an acceptor, and ferrocene was chosen as the donor. Both axial and peripheral functionalization was investigated using four different linker groups between the SubPc unit and the ferrocene unit. The calculated molecular orbitals were compared for the 12 structures and discussed in the context of possible electron transport through the system and the use in organic photovoltaics...
September 12, 2018: Journal of Physical Chemistry. A
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