In this paper we present a quantum mechanical model for direct photodissociation and for predissociation of polyatomic molecules in terms of a sequential decay scheme involving multiple coupled continua, where each continuum corresponds to a different internal vibrational state of the fragments. The coupling matrix elements between the “initial” state and the continuum states are in general determined by the appropriate vibrational overlap factors for the polyatomic radical, while intercontinua coupling for a triatomic molecule occurs only between adjacent vibrational continua. The time evolution of the system was handled by the Green's function method. Explicit theoretical expressions for the final vibrational distribution of the fragments in the photofragmentation of linear triatomic molecules were derived, which are determined by the initial coupling to the different continua and by a wave matrix which couples the various dissociative channels. The wave matrix was evaluated for some simple realistic models for the intercontinua coupling. The available experimental data for the vibrational distribution of the CN(B2Σ) radical resulting from photodissociation and predissociation of XCN molecules are well accounted for in terms of our theory.