Common classes of organic structures, including alkanes, alkenes, aromatics, primary, secondary and tertiary amines, amides, aldehydes, and carboxylic acids, were studied. Binding energies between SO2, Hgo and each organic molecule were calculated quantum mechanically (QM), using B3LYP and X3LYP flavors of Density Functional Theory (DFT). In addition, scans of the potential energy surfaces between these various organic molecules and SO2 and Hgo were performed, and the van der Waals interactions were fit to develop a first principles force field (Morse potential), for use in molecular dynamics (MD) simulations. The forcefield parameters were calculated for various atom types in the organic molecules, such as carbon (sp3, sp2, sp hybridized), nitrogen (sp3, sp), oxygen (sp2), for example; for their interactions with the sulfur, oxygen and mercury atoms in SO2, Hgo.
The QM binding energy results for the organic-SO2, Hgo systems were analyzed for their van der Waals and electrostatic energy contributions. The calculated QM binding energies for organic-SO2 systems indicate that the organics that show strong binding with SO2 are ones containing amine, amide and acid groups. Weak or no binding of SO2 was observed with alkane, alkene, and aromatics. The binding energies for organic-Hgo systems showed that the only organics that had any binding are primary and secondary amines, which showed only weak binding. All other organic molecules showed repulsive interactions with Hgo.
The organic molecules considered in this study are considered to be a part of a polymer chain, either in the backbone or as side groups. The methodology has been successfully used for rapid quantum screening of polymer based sensing materials in the JPL Electronic Nose (ENose).
Keywords: Quantum mechanics, Density Functional Theory, Binding Energy, Organics, Mercury, Sulfur dioxide, Computational material screening, Environmental monitoring