Proceedings - Interdisciplinary Center for Nanotoxicity

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118 Conference on Current Trends in Computational Chemistry 2009 Nonlinear Optical Properties of Triangular Silver Nanomaterials Anant Kumar Singh, Dulal Senapati, Adria Neely, Gabriel Kolawole and Paresh Chandra Ray* Department of Chemistry and Biochemistry, Jackson State University, Jackson, MS, USA Shape‐controlled synthesis of metal nanostructures has opened many new possibilities to design ideal building blocks for future nanodevices. By solution‐based method, silver triangular nanoprisms of different sizes (edge length) have been synthesized. First hyper‐polarizabilities of silver triangular nanomaterials were measured using hyper‐Rayleigh scattering technique. We have shown that both linear and nonlinear optical properties are highly depends on the size of silver triangular nanoprism. We provide experimental evidence for higher multipolar contribution to NLO response of silver nanoprism.
Conference on Current Trends in Computational Chemistry 2009 A Comprehensive Study on Decomposition of Nitrous Oxide over Extra‐framework Aluminum Species in ZSM‐5 Zeolite: MP2 versus DFT/B3LYP Vitaly Solkan and Jerzy Leszczynski N. D. Zelinski Institute of Organic Chemistry, RAS, 119991 Moscow, Leninskii pr. 47, Russian Federation; Email: solkanvn@ioc.ac.ru Interdisciplinary Center for Nanotoxicity, Department of Chemistry and Biochemistry, Jackson State University, P.O. Box 17910, 1325 Lynch Str., Jackson, MS 39217, USA. Nitrous oxide (N2O) is a potent greenhouse gas and contributes to ozone layer depletion. This has prompted the development of several abatement technologies based mainly on the catalytic decomposition. Recently we presented DFT/B3LYP study of the interaction of nitrous oxide with Ga/ZSM‐5 and GaO/ZSM‐5 [1]. The active centers were taken to be mononuclear [Ga] + and [Ga=O] + . We shoved that the first step of N2O decomposition involves the formation of [GaO] + and the release of N2. The metal‐oxo species produced in this step then reacts with N2O again, to release N2 and form [GaO2] + . The calculated activation energies for N2O dissociation in Ga‐ZSM‐5 and GaO‐ZSM‐5 are 22.2 and 24.9 kcal/mol, respectively. In the present work we have performed a detailed theoretical study of the mechanisms of nitrous oxide dissociation in Al‐ZSM‐5, AlO‐ZSM‐5, and AlO2‐ZSM‐5 using post‐Hartree‐Fock calculations at MP2/6‐31+G(d) computational level. Moreover, the reaction mechanism for nitrous oxide decomposition has been studied on aluminum site in Al‐ZSM‐5 using the DFT/B3LYP/6‐31+G(d) method. The active centers were taken to be mononuclear [Al] + , [Al=O] + , and [AlO2] + and the surrounding portion of the zeolite was represented by a 3T cluster, namely [AlSi2O4H8] ‐ . The stationary point energies (well‐depth corresponding to the reactant complex, ERC, transition state (TS) energies with respect to the reactant complex, E ) were evaluated at the B3LYP and MP2 levels. These energies were then corrected for zero‐point vibrational energies ( EZPVE) and for thermal energies ( H), and applied entropies to obtain free energies ( G) at 298 K. To check the effects of basis set superposition errors (BSSEs), the counterpoise correction method was applied to the addition complexes. To obtain more reliable values of the energies for the different stationary points on the PES, a number of single‐ point calculations using MP4(SDTQ) was performed. To verify the relevance of the transition states found, intrinsic reaction coordinate IRC calculations were performed starting from the transition states. The first elementary step of N2O decomposition involves the formation of [AlO] + and the release of N2. The metal‐oxo species produced in this step then reacts with N2O again, to release N2 and form [AlO2] + . The calculated activation energies at DFT/B3LYP level for N2O dissociation on Al‐ZSM‐5 and AlO‐ZSM‐5 are 9.86 and 15.07 kcal/mol at 298 K, respectively. The third elementary step of N2O decomposition on AlO2‐ZSM‐5 involves the formation of [AlO3] + and the release of N2. The calculated activation energy at DFT/B3LYP level for N2O dissociation on AlO2‐ZSM‐5 is 18.24 kcal/mol. Four‐order perturbation theory (MP4// DFT/B3LYP) predicts that the activation barriers for nitrous oxide dissociation at 298 K on Al‐ ZSM‐5, AlO‐ZSM‐5, and AlO2‐ZSM‐5 are 13.97, 17.89, and 32.71 kcal/mol, respectively. The calculated energy for desorption of singlet O2 from the 3T ‐ [OAl(O)2] + cluster at DFT/B3LYP level is 57.8 kcal/mol. When one takes into account the entropy gained upon desorption of singlet 119
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Proceedings - Interdisciplinary Center for Nanotoxicity

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