COMP 374 |
| Molecular Dynamics simulations, carried out “on the fly” for potentials from electronic structure calculations are reported for several thermal and photochemical processes of molecules in water and other clusters. For the relatively small clusters, the reliable MP2 ab initio method is used, while for larger clusters most simulations employ the semi-empirical PM3, modified for a more realistic description of some of the processes. The simulations provide insights into the mechanisms, rates and yields of the processes, and are suggestive as to their potential importance in atmospheric conditions. The processes studied include: (a) Overtone induced reactions of HONO and HNO3 at interfaces. It is concluded that for surfaces that bind strongly to the molecule (e.g. H2O for HNO3) the chemical reaction is suppressed, but for the cases of weak binding (HONO on H2O ), photochemistry is predicted to take place. (b) The neutralization of H+ and NO3- is found to take place on sub-picosecond timescales in small clusters. HNO3 is found to be a weak acid in these systems. (c) Hydrolysis of N2O4 at water clusters is studied, and the result supports the mechanism proposed by Finlayson-Pitts and coworkers, in particular a step involving dissociation of an isomer of N2O4 into ions. The result shows the power of on the fly simulations with suitable ab initio potentials in studies of chemical reactivity in condensed phases. This work was done in the framework of the NSF-sponsored Air-UCI project at UC Irvine.
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Recent Advances in Studies of Molecular Processes at Interfaces
8:30 AM-11:50 AM, Wednesday, August 22, 2007 BCEC -- 156C, Oral
Division of Computers in Chemistry |