PHOTO INDUCED 3 BODY DECAY

The photo induced three body decay: ABC + hv --> A + B + C, where a mo lecule ABC decays into three fragments A, B and C upon irradiation, is reviewed. Various experimental and theoretical techniques for the inv estigation of this reaction and their application to a wide range of m olecular species are discussed. Emphasis is laid on the distinction be tween concerted and stepwise processes, consisting of one single or tw o consecutive kinetic events, respectively. The concerted fragmentatio n scheme is further classified as being of either synchronous or async hronous character, depending on whether or not the bond breaking proce sses take place in unison. The three body decays of acetone, azomethan e and s-tetrazine are discussed in detail as prototypes for these mech anisms. A novel kinematic analysis approach, based on the evaluation o f fragment kinetic energy distributions, is presented and applied to t he ultraviolet photodissociation of phosgene. Competing pathways are f ound to be operative, dominated by the asynchronous concerted mechanis m with preferential forward scattering of the carbon monoxide fragment . The synchronous concerted decay plays a minor role under significant excitation of the in-plane and out-of-plane bending modes of the pare nt molecule. Finally the power of the newly developed method for the a nalysis of the three body decay of a small polyatomic molecule is high lighted.