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Journal of Physical Chemistry. A

Gunter Hermann, Yan Zhang, Bernhard Wassermann, Henry Fischer, Marcel Quennet, Eckart Ruehl
The influence of electrical excess charges on the crystallization from supersaturated aqueous sodium chloride solutions is reported. This is accomplished by efflorescence studies on single levitated microdroplets using optical and electrodynamic levitation. Specifically, a strong increase in efflorescence humidity is observed as a function of the droplet's negative excess charge, ranging up to -2.1 pC, with a distinct threshold behavior, increasing the relative efflorescence humidity, at which spontaneous nucleation occurs, from 44% for the neutral microparticle to 60%...
August 16, 2017: Journal of Physical Chemistry. A
Jia-Syun Lu, Ming-Chung Yang, Ming-Der Su
The effect of substitution on the potential energy surfaces of triple-bonded RGa≡PR (R = F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2, Tbt (C6H2-2,4,6-{CH(SiMe3)2}3), and Ar* (C6H3-2,6-(C6H2-2,4,6-i-Pr3)2)) compounds was theoretically examined by using the density functional theory (i.e., M06-2X/Def2-TZVP, B3PW91/Def2-TZVP and B3LYP/LANL2DZ+dp). The theoretical evidences strongly suggest all of the triple-bonded RGa≡PR species prefer to select a bent form with an angle (∠Ga-P-R) of about 90°. Moreover, the theoretical observations indicate only the bulkier substituents, in particular for the strong donating groups (e...
August 16, 2017: Journal of Physical Chemistry. A
Lisa Götte, Krista M Parry, Wei Hua, Dominique Verreault, Heather C Allen, Douglas J Tobias
The ion distribution and ion pairing properties of Mg(2+), SO4(2-), NO3(-), and Cl(-) in the interfacial region of MgSO4, Mg(NO3)2, and MgCl2 solutions were investigated using vibrational sum frequency generation (VSFG) spectroscopy and molecular dynamics (MD) simulations. An electric field reversal relative to Mg(NO3)2 and MgCl2 solutions is observed at the interface of a MgSO4 solution. We show that, although magnesium cations are expected to have preference for bulk solvation, solvent-shared ion pairs (SIPs) exist in the interfacial region in which Mg(2+) cations are closer to the solution surface than sulfate anions...
August 16, 2017: Journal of Physical Chemistry. A
Balmukund Sureshkumar Thakkar, John S M Svendsen, Richard Alan Engh
Cis/trans isomerization of 2º-amide bonds is a key step in a wide range of important processes. Here we present a theoretical assessment of cis/trans isomerization of 2º-amide bonds using B3LYP density functional methods, describing two reaction paths and corresponding geometry changes during isomerization of N-methylacetamide (NMA) and glycylglycine methyl ester (GGMe). The isomerization begins via a common path, as the extended π-bonding of the amide bond maintains approximate planarity of the O-C-N-H dihedral angle, with only gradually increasing pyramidalization of the nitrogen atom, until a bifurcation point is reached...
August 15, 2017: Journal of Physical Chemistry. A
Richard N Collins, Kevin M Rosso
Molecular-level pathways in the aqueous redox transformation of uranium by iron remain unclear, despite the importance of this knowledge for predicting uranium transport and distribution in natural and engineered environments. As the relative importance of homogeneous versus heterogeneous pathways is difficult to probe experimentally, here we apply computational molecular simulation to isolate rates of key one electron transfer reactions in the homogenous pathway. By comparison to experimental observations the role of the heterogeneous pathway also becomes clear...
August 15, 2017: Journal of Physical Chemistry. A
Boris Bazanov, Uzi Geiger, Dan Grinstein, Shmuel Welner, Yehuda Haas
The cyclopentazolate anion, N5-, has been researched extensively over the years and detected in the gas phase more than a decade ago, but was only recently measured in solution. The process whereby aryl pentazole reduction leads to the production of N5- is still not fully understood. Here, the production of N5- in solution was investigated using isotopic labeling techniques while implementing changes to the synthesis methodologies. 15N labeled phenyl pentazole produced appropriately labeled phenyl pentazole radical anions and N5- which, upon collision induced dissociation, produced the expected N3- signals...
August 15, 2017: Journal of Physical Chemistry. A
Tatiana V Esipova, Héctor J Rivera-Jacquez, Bruno Weber, Artëm E Masunov, Sergei A Vinogradov
Using time-dependent density functional theory (TDDFT) and sum-overstates (SOS) formalism, we predicted significant stabilization of 2P-active g-states in a compact fully symmetric porphyrin, in which all four pyrrolic fragments are fused with phathalimide residues via the β-carbon positions. The synthesis of a soluble, nonaggregating meso-unsubstituted tetraarylphthalimidoporphyrin (TAPIP) was then developed, and the spectroscopic measurements confirmed that a strongly 2P-active state in this porphyrin is stabilized below the B (Soret) state level...
August 15, 2017: Journal of Physical Chemistry. A
Dudley R Herschbach, John G Loeser, Wilton L Virgo
Melding quantum and classical mechanics is an abiding quest of physical chemists who strive for heuristic insights and useful tools. We present a surprisingly simple and accurate treatment of ground-state two-electron atoms. It makes use of only the dimensional dependence of a hydrogen atom, together with the exactly known first-order perturbation value of the electron-electron interaction, both quintessentially quantum, and the D → ∞ limit, entirely classical. The result is an analytic formula for D-dimensional two-electron atoms with Z ≥ 2...
August 15, 2017: Journal of Physical Chemistry. A
Xiaozhou Yu, Haoming Yan, Qing Peng
Pyridine molecules have been used to passivate the surface Pb2+ sites of CH3NH3PbI3, to recrystallize CH3NH3PbI3, and to bleach CH3NH3PbI3. These results contradict each other as recrystallization and optical-bleach require transformation of bulk CH3NH3PbI3, but surface passivation demands the confinement of the reaction at the surface region. The underlying mechanism for these seemly contradicting results are not yet understood. In this paper, we show, at 25 ºC, partial pressure of pyridine vapor is a determining factor for its reaction behaviors with CH3NH3PbI3: one can modify the surface region of CH3NH3PbI3 by using pyridine vapor of pressure 1...
August 14, 2017: Journal of Physical Chemistry. A
Kamila Klajman, Grzegorz Ciepielowski, Rafal Kaminski, Paweł Adamczyk, Piotr Paneth
We have performed calculations of possible oxidation pathways of 4-nitrotoluene (4NT) by permanganate anion and evaluated relative contributions of oxidation of the methyl group and aromatic ring. Although a few theory levels matched experimental results obtained by Compound Specific Isotope Analysis (CSIA) for 4NT, they failed in reproducing results for other nitrotoluene derivatives studied previously[Wijker, R.S.; Adamczyk, P.; Bolotin, J.; Paneth, P.; Hofstetter, T.B. Environ. Sci. Technol., 2013, 47, 13459-13468]...
August 14, 2017: Journal of Physical Chemistry. A
Isuru R Ariyarathna, Evangelos Miliordos
To reveal the diverse chemistry of beryllium we employ multi-reference methodologies to study the ground and several excited electronic states of the titled beryllium oxides and carbonyls. The two types of complexes serve as model systems to describe the various ways that beryllium can form chemical bonds. Be(O2), its isomer OBeO, and Be(O2)2 are ionic compounds where beryllium is best represented in its Be(II) oxidation state. On the other hand, CO induces the excitation of one or two 2s electrons of beryllium to its 2p shell...
August 14, 2017: Journal of Physical Chemistry. A
Jonathan D Adams, Preston G Scrape, Shih-Huang Lee, Laurie J Butler
These experiments report the dissociative photoionization of vinoxy radicals to m/z = 15 and 29. In a crossed laser-molecular beam scattering apparatus, we induce C-Cl bond fission in 2-chloroacetaldehyde by photoexcitation at 157 nm. Our velocity measurements, combined with conservation of angular momentum, show that 21% of the C-Cl photofission events form vinoxy radicals that are stable to subsequent dissociation to CH3 + CO or H + ketene. Photoionization of these stable vinoxy radicals, identified by their velocities, which are momentum-matched with the higher-kinetic-energy Cl atom photofragments, shows that the vinoxy radicals dissociatively photoionize to give signal at m/z = 15 and 29...
August 14, 2017: Journal of Physical Chemistry. A
Dmitry Vasilievich Korabel'nikov, Yuriy N Zhuravlev
The structural and electronic properties of oxyanionic crystalline hydrates, LiNO3•3H2O, LiClO4•3H2O and NaClO4•H2O, have been studied using density functional theory including van der Waals interactions. It is established that the linear compressibility of lithium perchlorate trihydrate is anisotropic (a < c) and positive, while lithium nitrate trihydrate and sodium perchlorate monohydrate demonstrate negative linear compressibility along the b and c- axes, respectively. Deformation of Ow-H•••O hydrogen bonding motifs is correlated with the negative linear compressibility...
August 14, 2017: Journal of Physical Chemistry. A
Adrian F Tuck
Proposed Empirical Entropy and Gibbs Energy Based on Observations of Scale Invariance in Open Non-Equilibrium Systems Abstract There is no widely agreed definition of entropy, and consequently Gibbs energy, in open systems far from equilibrium. One recent approach has sought to formulate an entropy and Gibbs energy based on observed scale invariances in geophysical variables, particularly in atmospheric quantities, including the molecules constituting stratospheric chemistry. The Hamiltonian flux dynamics of energy in macroscopic open non-equilibrium systems maps to energy in equilibrium statistical thermodynamics, and corresponding equivalences of scale invariant variables with other relevant statistical mechanical variables such as entropy, Gibbs energy and 1/(kBoltzmannT) are not just formally analogous but are also mappings...
August 14, 2017: Journal of Physical Chemistry. A
Brett A McGuire, Marie-Aline Martin-Drumel, Michael C McCarthy
Supercritical CO2 is an appealing nontoxic, environmentally friendly solvent for the industrial extraction of many classes of compounds, from caffeine to natural product drug precursors to petrochemical impurities. Apolar in isolation, the ability of supercritical CO2 to dissolve polar species has been empirically shown to be greatly enhanced by the addition of a small molar percentage of a polar cosolvent, often ethanol. Computational work predicts that the isolated ethanol-CO2 complex can exist either in an electron-donor configuration or through a hydrogen-bonding one; yet, neither has been previously experimentally observed...
August 14, 2017: Journal of Physical Chemistry. A
Martta Toivola, Nønne L Prisle, Jonas Elm, Eleanor M Waxman, Rainer Volkamer, Theo Kurtén
We have used COSMO-RS, a method combining quantum chemistry with statistical thermodynamics, to compute Setschenow constants (KS) for a large array of organic solutes and salts. These comprise both atmospherically relevant solute-salt combinations, as well as systems for which experimental data are available. In agreement with previous studies on single salts, the Setschenow constants predicted by COSMO-RS (as implemented in the COSMOTherm program) are generally too large compared to experiments. COSMOTherm overpredicts salting out (positive KS), and/or underpredicts salting in (negative KS)...
August 14, 2017: Journal of Physical Chemistry. A
Mannix Padayhag Balanay, Dong Hee Kim
Bacteriochlorin-based dyes, having a push-pull type of configuration similar to the YD2 dye, were theoretically designed based on the modification of the macrocycle and π-conjugated bridge for use in dye-sensitized solar cells. Various parameters were assessed to determine its structure-property relationships, such as the absorption profile based on time-dependent density functional theory, non-linear optical properties from (hyper)polarizability data, ground- and excited-state oxidation potentials, and the electronic properties of the free and adsorbed dyes...
August 11, 2017: Journal of Physical Chemistry. A
Lin Wang, Tatsuya Ishiyama, Akihiro Morita
Using the flexible and polarizable model in the preceding paper I, we performed comprehensive analysis of C-H stretching vibrations of ethanol and partially deuterated ones by molecular dynamics (MD) simulation. The overlapping band structures of C-H stretching region including (i) methyl and methylene, (ii) number of modes with Fermi resonances, and (iii) different trans/gauche conformers are disentangled by various analysis methods, such as isotope exchange, empirical potential parameter shift analysis, and separate calculations of conformers...
August 11, 2017: Journal of Physical Chemistry. A
Lu Han, Daniela Iguchi, Phwey Gil, Tyler R Heyl, Victoria M Sedwick, Carlos R Arza, Seishi Ohashi, Daniel J Lacks, Hatsuo Ishida
Polymerization of benzoxazine resins is indicated by the disappearance of a 960-900 cm(-1) band in infrared spectroscopy (IR). Historically, this band was assigned to the C-H out-of-plane bending of the benzene to which the oxazine ring is attached. This study shows that this band is a mixture of the O-C2 stretching of the oxazine ring and the phenolic ring vibrational modes. Vibrational frequencies of 3-phenyl-3,4-dihydro-2H-benzo[e][1,3]oxazine (PH-a) and 3-(tert-butyl)-3,4-dihydro-2H-benzo[e][1,3]oxazine (PH-t) are compared with isotope-exchanged and all-substituted compounds...
August 11, 2017: Journal of Physical Chemistry. A
Andrew S Khalil, Anne-Marie Kelterer, Richard J Lavrich
This combined experimental and theoretical study answers the question whether the intramolecular hydrogen bond strength in amino alcohols is dependent on the ring size. For this purpose, the rotational spectrum of the 3-aminopropanol-H2O van der Waals complex was recorded using Fourier-transform microwave spectroscopy and fit to the rotational, quadrupole coupling, and centrifugal distortion constants of the Watson A-reduction Hamiltonian. The experimental results are consistent with an ab initio conformation calculated at the MP2/6-311++G(d,p) level that involves the lowest energy 3-aminopropanol monomer and consists of a hydrogen bonding network...
August 10, 2017: Journal of Physical Chemistry. A
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