Browsing by Author "Chapleski, Robert C. Jr."
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- Atomic-Level Structural Dynamics of Polyoxoniobates during DMMP DecompositionWang, Qi; Chapleski, Robert C. Jr.; Plonka, Anna M.; Gordon, Wesley O.; Guo, Weiwei; Thuy-Duong Nguyen-Phan; Sharp, Conor H.; Marinkovic, Nebojsa S.; Senanayake, Sanjaya D.; Morris, John R.; Hill, Craig L.; Troya, Diego; Frenkel, Anatoly I. (Springer Nature, 2017-04-10)Ambient pressure in situ synchrotron-based spectroscopic techniques have been correlated to illuminate atomic-level details of bond breaking and formation during the hydrolysis of a chemical warfare nerve agent simulant over a polyoxometalate catalyst. Specifically, a Cs-8[Nb6O19] polyoxoniobate catalyst has been shown to react readily with dimethyl methylphosphonate (DMMP). The atomic-level transformations of all reactant moieties, the [Nb6O19](8)-polyanion, its Cs+ counterions, and the DMMP substrate, were tracked under ambient conditions by a combination of X-ray absorption fine structure spectroscopy, Raman spectroscopy, and X-ray diffraction. Results reveal that the reaction mechanism follows general base (in contrast to specific base) hydrolysis. Together with computational results, the work demonstrates that the ultimate fate of DMMP hydrolysis at the Cs-8[Nb6O19] catalyst is strong binding of the (methyl) methylphosphonic acid ((M) MPA) product to the polyanions, which ultimately inhibits catalytic turnover.
- Heterogeneous chemistry and reaction dynamics of the atmospheric oxidants, O3, NO3, and OH, on organic surfacesChapleski, Robert C. Jr.; Zhang, Yafen; Troya, Diego; Morris, John R. (The Royal Society of Chemistry, 2015-11-11)Heterogeneous chemistry of the most important atmospheric oxidants, O3, NO3, and OH, plays a central role in regulating atmospheric gas concentrations, processing aerosols, and aging materials. Recent experimental and computational studies have begun to reveal the detailed reaction mechanisms and kinetics for gas-phase O3, NO3, and OH when they impinge on organic surfaces. Through new research approaches that merge the fields of traditional surface science with atmospheric chemistry, researchers are developing an understanding for how surface structure and functionality affect interfacial chemistry with this class of highly oxidizing pollutants. Together with future research initiatives, these studies will provide a more complete description of atmospheric chemistry and help others more accurately predict the properties of aerosols, the environmental impact of interfacial oxidation, and the concentrations of tropospheric gases.
- Theoretical Study of the Ozonolysis of C60: Primary Ozonide Formation, Dissociation, and Multiple Ozone AdditionsChapleski, Robert C. Jr.; Morris, John R.; Troya, Diego (The Royal Society of Chemistry, 2014-01-28)We present an investigation of the reaction of ozone with C60 fullerene using electronic structure methods. Motivated by recent experiments of ozone exposure to a C60 film, we have characterized stationary points in the potential energy surface for the reactions of O3 with C60 that include both the formation of primary ozonide and subsequent dissociation reactions of this intermediate that lead to C_C bond cleavage. We have also investigated the addition of multiple O3 molecules to the C60 cage to explore potential reaction pathways under the high ozone flux conditions used in recent experiments. The lowest-energy product of the reaction of a single ozone molecule with C60 that results in C_C bond breakage corresponds to an open-cage C60O3 structure that contains ester and ketone moieties at the seam. This open-cage product is of much lower energy than the C60O + O2 products identified in prior work, and it is consistent with IR experimental spectra. Subsequent reaction of the open-cage C60O3 product with a second ozone molecule opens a low-energy reaction pathway that results in cage degradation via the loss of a CO2 molecule. Our calculations also reveal that, while full ozonation of all bonds between hexagons in C60 is unlikely even under high ozone concentration, the addition of a few ozone molecules to the C60 cage is favorable at room temperature.