Isomers on the [H, S(2), Cl] potential energy surface: A high level investigation

This study reports a systematic state-of-the-art characterization of new sulfur-chlorine species on the [H, S(2), Cl] potential energy surface. Coupled cluster theory singles and doubles with perturbative contributions of connected triples, using the series of correlation consistent basis sets with extrapolations to the complete basis set limit (CBS), were employed to quantify the energetic quantities involved in the isomerization processes on this surface. The structures and vibrational frequencies are unique for some species and represent the most accurate investigation to date. These molecules are potentially a new route of coupling the sulfur and chlorine chemistries in the atmosphere, and conditions of high concentration of H(2)S (HS) like in volcanic eruptions might contribute to their formation. Also an assessment of the MP2/CBS approach relative to CCSD(T)/CBS provides insights on the expected performance of MP2/CBS on the characterization of polysulfides, and also of more complex systems containing disulfide bridges. (C) 2009 Elsevier B.V. All rights reserved.

Spin contamination in XOO radicals X = F, Cl, Br, HO: How is the investigation of the HOOO radical affected

We have analysed the effect of spin contamination in the wavefunction of HOOO. At least, two solutions can be found for the HF wavefunction. One, lower in energy, presents a high spin contamination and gives qualitatively incorrect structural parameters. On the other hand, the less contaminated HF reference gives structural parameters that are in better agreement with experiment, and positive spin densities on all atoms. Some of the problems described during previous investigations of HOOO can now be traced to problems in the HF reference. For the first time we report a CCSD(T) estimation of the structure of HOOO cis employing a HF reference with small spin contamination. (C) 2008 Elsevier B.V. All rights reserved.

A quantum chemical study on the formation of phosphorus mononitride

The chemical mechanism of the (1)PN formation was successfully studied by using the CCSD(T)/6-311++G(3df,3pd) level of theory. The (1)NH(3) + (3)PH and (4)P + NH(3) reaction paths are not energetically favorable to form the (1)PN molecule. However, the (3)NH + (3)PH, (4)N + (3)PH(3), (4)N + (3)PH, (4)P + (3)NH, and (4)P + (2)NH(2) reaction paths to form the (1)PN molecule are only energetically favorable by taking place through specific transition states to form the (1)PN molecule. The NH(3) + (3)PH, (4)N + (1)PH(3), NH(3) + (4)P, and (4)N + (2)PH(2) reactions are spin-forbidden and the probability of hopping for these reactions was estimated to be 0 by the Landau-Zener theory. This is the first detailed study on the chemical mechanism for the (1)PN formation. (C) 2009 Elsevier B.V. All rights reserved.

Accurate ab initio potential energy surfaces for the (3)A '' and (3)A ' electronic states of the O(P-3) plus HBr system

In this work, we report the construction of potential energy surfaces for the (3)A '' and (3)A' states of the system O(P-3) + HBr. These surfaces are based on extensive ab initio calculations employing the MRCI+Q/CBS+SO level of theory. The complete basis set energies were estimated from extrapolation of MRCI+Q/aug-cc-VnZ(-PP) (n = Q, 5) results and corrections due to spin-orbit effects obtained at the CASSCF/aug-cc-pVTZ(-PP) level of theory. These energies, calculated over a region of the configuration space relevant to the study of the reaction O(P-3) + HBr -> OH + Br, were used to generate functions based on the many-body expansion. The three-body potentials were interpolated using the reproducing kernel Hilbert space method. The resulting surface for the (3)A '' electronic state contains van der Waals minima on the entrance and exit channels and a transition state 6.55 kcal/mol higher than the reactants. This barrier height was then scaled to reproduce the value of 5.01 kcal/mol, which was estimated from coupled cluster benchmark calculations performed to include high-order and core-valence correlation, as well as scalar relativistic effects. The (3)A' surface was also scaled, based on the fact that in the collinear saddle point geometry these two electronic states are degenerate. The vibrationally adiabatic barrier heights are 3.44 kcal/mol for the (3)A '' and 4.16 kcal/mol for the (3)A' state. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4705428]

A theoretical study of SnF2+, SnCl2+, and SnO2+ and their experimental search

We present a detailed theoretical study of the stability of the gas-phase diatomic dications SnF2+, SnCl2+, and SnO2+ using ab initio computer calculations. The ground states of SnF2+, SnCl2+, and SnO2+ are thermodynamically stable, respectively, with dissociation energies of 0.45, 0.30, and 0.42 eV. Whereas SnF2+ dissociates into Sn2+ + F, the long range behaviour of the potential energy curves of SnCl2+ and SnO2+ is repulsive and wide barrier heights due to avoided crossing act as a kind of effective dissociation energy. Their equilibrium internuclear distances are 4.855, 5.201, and 4.852 a(0), respectively. The double ionisation energies (T-e) to form SnF2+, SnCl2+, and SnO2+ from their respective neutral parents are 25.87, 23.71, and 25.97 eV. We combine our theoretical work with the experimental results of a search for these doubly positively charged diatomic molecules in the gas phase. SnO2+ and SnF2+ have been observed for prolonged oxygen (O-16(-)) ion beam sputtering of a tin metal foil and of tin (II) fluoride (SnF2) powder, respectively, for ion flight times of about 10(-5) s through a magnetic-sector mass spectrometer. In addition, SnCl2+ has been detected for O-16(-) ion surface bombardment of stannous (tin (II)) chloride (SnCl2) powder. To our knowledge, SnF2+ is a novel gas-phase molecule, whereas SnCl2+ had been detected previously by electron-impact ionization mass spectrometry, and SnO2+ had been observed before by spark source mass spectrometry as well as by atom probe mass spectrometry. We are not aware of any previous theoretical studies of these molecular systems. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4758475]

Quantum Mechanical Study of Sulfuric Acid Hydration: Atmospheric Implications

The role of the binary nucleation of sulfuric acid in aerosol formation and its implications for global warming is one of the fundamental unsettled questions in atmospheric chemistry. We have investigated the thermodynamics of sulfuric acid hydration using ab initio quantum mechanical methods. For H2SO4(H2O)n where n = 1–6, we used a scheme combining molecular dynamics configurational sampling with high-level ab initio calculations to locate the global and many low lying local minima for each cluster size. For each isomer, we extrapolated the Møller–Plesset perturbation theory (MP2) energies to their complete basis set (CBS) limit and added finite temperature corrections within the rigid-rotor-harmonic-oscillator (RRHO) model using scaled harmonic vibrational frequencies. We found that ionic pair (HSO4–·H3O+)(H2O)n−1clusters are competitive with the neutral (H2SO4)(H2O)n clusters for n ≥ 3 and are more stable than neutral clusters for n ≥ 4 depending on the temperature. The Boltzmann averaged Gibbs free energies for the formation of H2SO4(H2O)n clusters are favorable in colder regions of the troposphere (T = 216.65–273.15 K) for n = 1–6, but the formation of clusters with n ≥ 5 is not favorable at higher (T > 273.15 K) temperatures. Our results suggest the critical cluster of a binary H2SO4–H2O system must contain more than one H2SO4 and are in concert with recent findings(1) that the role of binary nucleation is small at ambient conditions, but significant at colder regions of the troposphere. Overall, the results support the idea that binary nucleation of sulfuric acid and water cannot account for nucleation of sulfuric acid in the lower troposphere.

Ab Initio correlated all electron dirac-fock calculations for Eka-Francium Fluoride (E119F)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

New calculations of P(b) curves for 1s_\sigma excitation in low-Z (Z\le10) ion-atom scattering

Ab initio fully relativistic SCF molecular calculations of energy eigenvalues as well as coupling-matrix elements are used to calculate the 1s_\sigma excitation differential cross section for Ne-Ne and Ne-O in ion-atom collisions. A relativistic perturbation treatment which allows a direct comparison with analogous non-relativistic calculations is also performed.

Gaussian basis sets by generator coordinate Hartree-Fock method to ab initio calculations of electron affinities of enolates

The Generator Coordinate Hartree-Fock (GCHF) method is employed to generate uncontracted 15s and 18s11p gaussian basis sets for the H, C and O atoms, respectively. These basis sets are then contracted to 3s and 4s H atom and 6s5p, for C and O atoms by a standard procedure. For quality evaluation of contracted basis sets in molecular calculations, we have accomplished calculations of total and orbital energies in the Hartree-Fock-Roothaaii (HFR) approach for CH, C(2) and CO molecules. The results obtained with the uncontracted basis sets are compared with values obtained with the standard D95, 6-311G basis sets and with values reported in the literature. The 4s and 6s5p basis sets are enriched with polarization and diffuse functions for atoms of the parent neutral systems and of the enolates anions (cycloheptanone enolate, 2,5-dimethyleyelopentanone enolate, 4-heptanone enolate, and di-isopropyl ketone enolate) from the literature, in order to assess their performance in ab initio molecular calculations, and applied for calculations of electron affinities of the enolates. The calculations were performed at the DFT (BLYP and B3LYP) and HF levels and compared with the corresponding experimental values and with those obtained by using other 6-3 1 + +G((*)) and 6-311 + +G((*)) basis sets from literature. For the enolates studied, the differences between the electron affinities obtained with GCHF basis sets, at the B3LYP level, and the experimental values are -0.001, -0,014, -0.001, and -0.001 eV. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Thermoanalytical study of nimesulide and their recrystallization products obtained from solutions of several alcohols

Thermogravimetry, differential scanning calorimetry, and vibrational infrared spectroscopy were used to study nimesulide and its recrystallization products that were obtained from solutions of several alcohols. The thermoanalytical measurements were performed in both air and nitrogen atmospheres and the results suggest that, under the experimental conditions used in this paper, it was possible to obtain neither polymorphic nor pseudopolymorphic forms of this drug. In this investigation, quantum chemical approach methods were used to determine the molecular structures using the Becke three-parameter hybrid method and the Lee-Yang-Parr correlation functional. The performed molecular calculations were done with the Gaussian 09 routine and the theoretical calculation results were correlated with the experimental IR vibrational spectrum. © 2013 Akadémiai Kiadó, Budapest, Hungary.

Steps and bumps:precision extraction of discrete states of molecular machines

We report statistical time-series analysis tools providing improvements in the rapid, precision extraction of discrete state dynamics from time traces of experimental observations of molecular machines. By building physical knowledge and statistical innovations into analysis tools, we provide techniques for estimating discrete state transitions buried in highly correlated molecular noise. We demonstrate the effectiveness of our approach on simulated and real examples of steplike rotation of the bacterial flagellar motor and the F1-ATPase enzyme. We show that our method can clearly identify molecular steps, periodicities and cascaded processes that are too weak for existing algorithms to detect, and can do so much faster than existing algorithms. Our techniques represent a step in the direction toward automated analysis of high-sample-rate, molecular-machine dynamics. Modular, open-source software that implements these techniques is provided.

A multifunctional iridium carbazolyl orange phosphor for high performance two-element WOLED exploiting exciton-managed fluorescence/phosphorescence

By attaching a bulky, inductively electron-with drawing trifluoromethyl (CF3) group on the pyridyl ring of the rigid 2-[3(N-phenylcarbazolyl)]pyridine cyclometalated ligand, we successfully synthesized a new heteroleptic orange-emitting phosphorescent iridium(III) complex [Ir(L-1)(2)(acac)] 1 (HL1=5-trifluoromethyl-2-[3-(N-phenylcarbazolyl)]pyridine, Hacac = acetylacetone) in good yield.

Manipulating charge-transfer character with electron-withdrawing main-group moieties for the color tuning of iridium electrophosphors

A new and synthetically versatile strategy has been developed for the phosphorescence color tuning of cyclometalated iridium phosphors by simple tailoring of the phenyl ring of ppy (Hppy=2-phenylpyridine) with various main-group moieties in [Ir(ppy-X)(2)(acac)] (X=B(Mes)(2), SiPh3, GePh3, NPh2, POPh2, OPh, SPh, SO2Ph). This can be achieved by shifting the charge-transfer character from the pyridyl groups in some traditional iridium ppy-type complexes to the electron-withdrawing main-group moieties and these assignments were supported by theoretical calculations.