Influence of the medium on the kinetics of photo-radical chain reactions in a solid phase

An investigation has been made of photo-radical chain reactions in a solid phase, with frozen acetic anhydride and triethylamine as examples where the radicals carrying on the chain are CH3 and C2H5 alkyl radicals. The temperature dependence of the rate constants of dissociation of the excited radicals has been determined and accounted for. It is shown that the effective activation energy of the dissociation is greater the larger is the radical detached upon photodissociation. The influence of the medium on the kinetics of the photoradical chain processes is due both to the effect of the molecular environment on the dissociating radical and to the reorganization of the medium during the photodissociation