On the kinetic treatment of photochemically induced isotopic exchange

A kinetic treatment describing the time dependence of the exchanged fraction (F) is presented for the photochemically-induced isotopic exchange process: AX+BX^* → hvAX^*+BX when complicated by a net change in the concentration of AX due to the side reaction: AX → hvBX. The kinetic equations are numerically integrated and applied to the specific case in which AX ≡ iodobenzene and BX^* is radioactive iodine (I¹³¹I). The treatment accounts quantitatively for the experimental F vs. time plots. It also leads to the evaluation of the relative rate constants of the phenyl radical (Ph·) scavenging processes: Ph· + I₂→PhI+I. and Ph·+S→scavenging products where S is benzene, toluene or molecular oxygen.