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    Can sulfur-containing molecules solvate/ionize HCl? Solid state solvation of HCl on/in methanethiol clusters/nanoparticles
    (Aip Publishing, 2019) Uras-Aytemiz, Nevin; Balci, F. Mine; Devlin, J. Paul
    Solvation of HCl at <100 K at the surface of nanoparticles of methanethiol, a sulfur derivative of methanol, was investigated by FTIR spectroscopy and on-the-fly molecular dynamics as implemented in the density functional code QUICKSTEP (which is part of the CP2K package). Some of the results have been further checked with MP2-level ab initio calculations. Unlike the HCl-CH3OH system that has been examined before, HCl on the surface or within methanethiol nanoparticles does not achieve an ionized form. Requirements for acid solvation/ionization are discussed in context with the results for methanol clusters. Published under license by AIP Publishing.
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    CO2 and C2H2 in cold nanodroplets of oxygenated organic molecules and water
    (Aip Publishing, 2014) Devlin, J. Paul; Balci, F. Mine; Maslakci, Zafer; Uras-Aytemiz, Nevin
    Recent demonstrations of subsecond and microsecond timescales for formation of clathrate hydrate nanocrystals hint at future methods of control of environmental and industrial gases such as CO2 and methane. Combined results from cold-chamber and supersonic-nozzle [A. S. Bhabhe, Experimental study of condensation and freezing in a supersonic nozzle, Ph.D. thesis (Ohio State University, 2012), Chap. 7] experiments indicate extremely rapid encagement of components of all-vapor pre-mixtures. The extreme rates are derived from (a) the all-vapor premixing of the gas-hydrate components and (b) catalytic activity of certain oxygenated organic large-cage guests. Premixing presents no obvious barrier to large-scale conditions of formation. Further, from sequential efforts of the groups of Trout and Buch, a credible defect-based model of the catalysis mechanism exists for guidance. Since the catalyst-generated defects are both mobile and abundant, it is often unnecessary for a high percentage of the cages to be occupied by a molecular catalyst. Droplets represent the liquid phase that bridges the premixed vapor and clathrate hydrate phases but few data exist for the droplets themselves. Here we describe a focused computational and FTIR spectroscopic effort to characterize the aerosol droplets of the all-vapor cold-chamber methodology. Computational data for CO2 and C2H2, hetero-dimerized with each of the organic catalysts and water, closely match spectroscopic redshift patterns in both magnitude and direction. Though vibrational frequency shifts are an order of magnitude greater for the acetylene stretch mode, both CO2 and C2H2 experience redshift values that increase from that for an 80% water-methanol solvent through the solvent series to approximately doubled values for tetrahydrofuran and trimethylene oxide (TMO) droplets. The TMO solvent properties extend to a 50 mol.% solution of CO2, more than an order of magnitude greater than for the water-methanol solvent mixture. The impressive agreement between heterodimer and experimental shift values throughout the two series encourages speculation concerning local droplet structures while the stable shift patterns appear to be useful indicators of the gas solubilities. (C) 2014 AIP Publishing LLC.
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    A detailed hydrogen bonding analysis on the compositions of H2SO4/HNO3/H2O ternary systems: A computational study
    (Elsevier Science Inc, 2018) Balci, F. Mine; Uras-Aytemiz, Nevin
    Hydrogen bonding properties of H2SO4/HNO3/H2O ternary molecular clusters have been studied by means of structural, energetic, topological, and spectroscopic perspectives. The roles of the hydrogen bonds in the formation of these clusters are considered according to the molecule positions (proton donor or proton acceptor) in the clusters. 33 stable conformers were identified on the potential energy surface. The global minimum one was obtained when HNO3 donates a proton to H2SO4, however, the cooperativity effect contribution was found to be significant for the cluster where HNO3 acts as a proton donor to an H2O molecule. (C) 2017 Elsevier Inc. All rights reserved.
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    H-bonding behavior of ethylene oxide within the clathrate hydrates revisited: Experiment and theory
    (Elsevier, 2020) Maslakci, Zafer; Devlin, J. Paul; Uras-Aytemiz, Nevin
    FTIR spectroscopy has been used to reexplore the nonclassical behavior of ethylene oxide (EO) within the large cages of clathrate hydrates. In most of the spectroscopic studies of EO within the clathrate hydrate cages, the classical EO bands attributed to the C-O stretch mode of EO were misassigned. Therefore, the all-vapor subsecond approach to clathrate-hydrate formation combined with computational studies was used to reexamine spectroscopic characteristics of EO molecules in which they can be either in classical or nonclassical forms.
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    Hydration of HNO3-HOCl clusters: Bonding properties
    (Elsevier, 2014) Balci, F. Mine; Uras-Aytemiz, Nevin; Escribano, Rafael; Gomez, Pedro C.
    Molecular clusters of atmospheric relevance containing water and two acidic species, HNO3 and HOCl, are studied using several theoretical techniques, with especial emphasis on their bonding characteristics. Stable structures are found with a minimum in their potential energy surface for aggregates with three and four H2O molecules. In the most stable configurations the H atom of HNO3 is partly donated to the O atom of HOCl. A full proton transfer only takes place for some aggregates when four H2O molecules are present. Proton transfer parameters, electron density at the bond critical point, atomic charges and spectroscopic properties are studied for all these species, revealing direct relationships among several of these properties. The proton transfer parameter gives a straightforward indication of the degree of ionization of the aggregates, with negative or positive values for molecular or ionic (i.e. with fully ionized nitric acid) clusters, respectively. The calculated electron densities yield values typical of hydrogen bonded species. A linear correlation is found between proton transfer parameters and electron density values. Atomic charges are calculated using three different methods, namely Mulliken, Natural Bond Order, and Bader, with sometimes fairly large differences in the estimated values. The predicted spectra present large variations in wavenumber and intensity of the main bands, which could be used to identify specific aggregates among complex spectra. Finally, the effect of the strength of the chlorinated acidic species is evaluated by comparing the HOCl clusters studied here with similar aggregates containing HCl. The weaker acid favors a higher degree of proton sharing in HNO3. (C) 2014 Elsevier B.V. All rights reserved.
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    Hydrogen-bonding behavior of various conformations of the HNO3•••(CH3OH)2 ternary system
    (Springer, 2018) Ozsoy, Hasan; Uras-Aytemiz, Nevin; Balci, F. Mine
    Nine minima were found on the intermolecular potential energy surface for the ternary system HNO3(CH3OH)(2) at the MP2/aug-cc-pVDZ level of theory. The cooperative effect, which is a measure of the hydrogen-bonding strength, was probed in these nine conformations of HNO3 center dot center dot center dot(CH3OH)(2). The results are discussed here in terms of structures, energetics, infrared vibrational frequencies, and topological parameters. The cooperative effect was observed to be an important contributor to the total interaction energies of the cyclic conformers of HNO3 center dot(CH3OH)(2), meaning that it cannot be neglected in simulations in which the pair-additive potential is applied.
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    Molecular Modes and Dynamics of HCI and DCI Guests of Gas Clathrate Hydrates
    (Amer Chemical Soc, 2015) Uras-Aytemiz, Nevin; Balci, F. Mine; Maslakci, Zafer; Ozsoy, Hasan; Devlin, J. Paul
    Recent years have yielded advances in the placement of unusual molecules as guests within clathrate hydrates (CHs) without severe distortion of the classic lattice structures. Reports describing systems for which observable but limited distortion does occur are available for methanol, ammonia, acetone, and small ether molecules. In these particular examples, the large-cage molecules often participate as non-classical guests H-bonded to the cage walls. Here, we expand the list of such components to include HCl/DCl and HBr as small-cage guests. Based on FTIR spectra of nanocrystalline CHs from two distinct preparative methods combined with critical insights derived from on-the-fly molecular dynamics and ab initio computational data, a coherent argument emerges that these strong acids serve as a source of molecular small-cage guests, ions, and orientational defects. Depending on the HCl/DCl content the ions, defects and molecular guests determine the CH structures, some of which form in sub-seconds via an all-vapor preparative method.
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    NH3 as simple clathrate-hydrate catalyst: Experiment and theory
    (Aip Publishing, 2018) Kilic, Murat; Devlin, J. Paul; Uras-Aytemiz, Nevin
    The catalytic action of NH3 within the all-vapor approach for instant clathrate hydrate (CH) formation is studied using both FTIR spectroscopy and ab initio molecular dynamics simulations. A unique property of NH3, namely, the rapid abundant penetration and occupation of the water network, creates defects, particularly Bjerrum D-defects, in the hydrate frame that are generally stabilized by guest NH3 molecules in the cages. Furthermore, insertion of NH3 seriously disturbs the hydrate network where the guest NH3 molecules also make fluxional H-bonds with the host water molecules. These defects strongly facilitate a sub-second formation of the simple NH3 s-II gas hydrate at 160 K. FTIR spectra of aerosols of the NH3 s-II CH have been measured, and the displacement of both small and large cage NH3 guests by CO2 and tetrahydrofuran is examined. Published by AIP Publishing.
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    NH3 as unique non-classical content-former within clathrate hydrates
    (Aip Publishing, 2017) Maslakci, Zafer; Devlin, J. Paul; Uras-Aytemiz, Nevin
    High quality FTIR spectra of aerosols of NH3-THF and NH3-TMO binary clathrate hydrates (CHs) have been measured. Our recently developed all-vapor sub-second approach to clathrate-hydrate formation combined with computational studies has been used to identify vibrational spectroscopic signatures of NH3 within the gas hydrates. The present study shows that there are three distinct NH3 types, namely, classical small-cage NH3, nonclassical small-cage NH3, and NH3 within the hydrate network. The network ammonia does not directly trigger the non-classical CH structure. Rather, the ammonia within the network structure perturbs the water bonding, introducing orientational defects that are stabilized by small and/or large cage guest molecules through H-bonding. This unusual behavior of NH3 within CHs opens a possibility for catalytic action of NH3 during CH-formation. Furthermore, impacts over time of the small-cage NH3-replacement molecules CO2 and CH4 on the structure and composition of the ternary CHs have been noted. Published by AIP Publishing.