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 pa rts of the mechanism by a number of experimental methods, all of which rely upon the experimental evaluation of the stationary-state Jacobia n matrix elements (JMEs). If the response by all species to a pulse pe rturbation of one of the species can be measured, then it is possible to determine all of the JMEs. A different experimental method, a conce ntration shift experiment, relies on measuring the change of steady-st ate concentrations in a chemical reactor after the inflow of each spec ies has been altered. Another technique employs the induction (or cess ation) of oscillations caused by a delayed feedback imposed on an infl ow species. If we assume power law kinetics, the connectivity of the r eaction network can be determined on the basis of the signs of the JME s. 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 o f the suggested reaction rates can be calculated from the measured JME s. The method of constructing a mechanism is illustrated with JMEs cal culated from a model of the horseradish peroxidase reaction. If the in verse of the Jacobian (the concentration shift matrix) or the phase sh ifts between pairs of oscillating species can be measured, the species in the oscillatory reaction can be classified and the reaction mechan ism can be categorized. If, due to experimental constraints, the entir e Jacobian cannot be evaluated, these methods offer a new series of te sts that must be passed by any proposed mechanism. Qualitative determi nation, such as the signs of JMEs, can also be useful.