Photoinduced Near Ultraviolet Three Body Decay of Phosgene

Abstract

Faced with the problem of underdetermined kinetic equations in analyzing momenta and kinetic energies of three body decay fragments, we followed two conceptually different paths in order to shed light on the dynamics of the process. One is based on the evaluation of the observed kinematic quantities after introduction of physically meaningful parameters for each type of decay: sequential, synchronously concerted, and asynchronously concerted mechanism. The other one is based on an information theoretic approach, maximizing the entropy of the joint probability matrix containing the probabilities for coincidently realizing accessible sets of product states. The results obtained in both cases match remarkably well: No significant contribution of a molecular channel, producing chlorine molecules, was found. Likewise, the generation of a stable chloroformyl radical had been ruled out in previous studies, so that every dissociation process upon irradiation around 230 nm yields three fragments: two chlorine atoms and a carbon monoxide molecule. For this three body decay, the asynchronously concerted mechanism is the dominant dissociation channel, accounting for over 80% of the products. The chlorine fragments move preferentially in the same direction, resulting in forward scattering of the carbon monoxide. A less abundant decay channel is the synchronously concerted mechanism, in which the two bonds cleave in unison, and that accounts for the remaining products. The geometry of the decaying parent resembles the ground state equilibrium geometry with significant excitations of the COCl2 bending modes. For both mechanisms the CO fragments are generated with high internal excitation.