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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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    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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    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.