QUINONE PHOTOREDUCTION .I. A MATHEMATICAL MODEL

The mechanism of photoreduction of semiquinones in hydrogen donor solutions (Q + RH2 →hv QH2 + R) has been the subject of many investigations.2 The simultaneous photoreduction of two quinones offers special opportunities for determining this mechanism because of the similarity to a titration in which first one then the other quinone is reduced. The point at which both quinones absorb the light equally resembles a midpoint." In this paper we present a method for determining rate constants of a 24-step mechanism which describes this process. The intermediate concentrations are calculated at each step of the integration (Runge-Kutta) for products. Difficulties arising from rapid concentration changes near the midpoint are overcome by making one of the product concentrations the independent variable and time a dependent variable."