SCAVENGER KINETICS AND THE LAPLACE TRANSFORM RELATIONSHIP .2. NONHOMOGENEOUS KINETICS

Laplace transform (LT) techniques are widely used in radiation chemistry to reconstruct nonhomogeneous kinetics from product yields in scavenger competition experiments. These techniques are tested using both stochastic and deterministic methods for a variety of systems where they formally break down, either because of the time dependence of the scavenging rate constant or because of the nonlinearity of the recombination kinetics. It is shown that the method can bc corrected exactly for the time dependence of the scavenging rate constant by a simple exchange of timescale. For a single isolated pair where both particles are scavengable another timescale change suffices to make the LT relationship exact. However, for multipair spurs the magnitude of any discrepancy is found to depend on the relative importance of the different combination reactions in the spur. If the recombination of unlike particles is relatively more important than the combination of like particles, as in the radiolysis of water, the discrepancies are small; however, if combination of like particles is important the LT method significantly underestimates the short time kinetics. The usual experimental procedure of fitting a function to the scavenged yield and inverting the LT is also investigated, and found to be generally reliable if the data extend to sufficiently high concentrations to cover the inflection in the scavenged yield, or if the initial yield is already known.