Seminar Synopses

New Developments in Semiempirical Quantum Chemical Methods
Walter Thiel
Organisch-Chemisches Institut
Universit ät Zurich
Zurich, Switzerland

Recent methodological developments in Professor Thiel's group include the extension of modified neglect of diatomic overlap (MNDO) molecular orbital theory to d orbitals, an approach to go beyond the MNDO model by incorporating additional one-electron terms (orthogonalization corrections, penetration integrals, and effective core potentials) and the combination of semiempirical methods with molecular mechanics (MM3). The lecture addressed the theory and parametrization of these approaches, the statistical evaluation of the results, and selected applications to large carbon clusters.

Transport Phenomena, Kinetics, and Safety in Oxidation Reactors for Chemical and Materials Synthesis
Dionisios Vlachos
Department of Chemical Engineering
University of Massachussets
Amherst, Massachussets

Homogeneous combustion of fossil fuels to form carbon dioxide and water (complete oxidation) is widely used for energy production, and a considerable effort is devoted to the understanding of homogeneous oxidation processes for improved energy efficiency with reduced pollutants. Heterogeneous reactors, on the other hand, convert fuels into valuable chemicals and materials by partial oxidation. At present, most oxidation systems are operated conservatively due to strong nonlinear responses in parameter space and to safety issues. Mathematical modeling offers a systematic way to study these problems.

The interplay of transport phenomena and kinetics in flame stability was examined for premixed hydrogen/air mixtures using sensitivity analysis and by comparing two model systems: a stagnation point flow reactor (a distributed system) with a well mixed reactor (a lumped system). A second-order finite difference scheme was employed to discretize the differential equations, and a weighted arc-length continuation technique was used to handle convergence problems in multicomponent reacting flows. A new approach for reduction of complex kinetic mechanisms was presented, and the role of catalysts in flame stability was also discussed.