TOWARD A SYSTEMATIC DETERMINATION OF COMPLEX-REACTION MECHANISMS

Given a complex chemical reaction with an unknown or a partially known mechanism, we examine the possibility of determining the essential parts of the mechanism by a number of experimental methods, all of which rely upon the experimental evaluation of the stationary-state Jacobian matrix elements (JMEs). If the response by all species to a pulse perturbation of one of the species can be measured, then it is possible to determine all of the JMEs. A different experimental method, a concentration shift experiment, relies on measuring the change of steady-state concentrations in a chemical reactor after the inflow of each species has been altered. Another technique employs the induction (or cessation) of oscillations caused by a delayed feedback imposed on an inflow species. If we assume power law kinetics, the connectivity of the reaction network can be determined on the basis of the signs of the JMEs. Once the connectivity of the reaction network has been established, then, with some knowledge of basic chemistry, the essential parts of the mechanism can be constructed. Furthermore, the rate coefficients of the suggested reaction rates can be calculated from the measured JMEs. The method of constructing a mechanism is illustrated with JMEs calculated from a model of the horseradish peroxidase reaction. If the inverse of the Jacobian (the concentration shift matrix) or the phase shifts between pairs of oscillating species can be measured, the species in the oscillatory reaction can be classified and the reaction mechanism can be categorized. If, due to experimental constraints, the entire Jacobian cannot be evaluated, these methods offer a new series of tests that must be passed by any proposed mechanism. Qualitative determination, such as the signs of JMEs, can also be useful.