Quantal-classical correspondence impulse theory

The quantal impulse cross section is derived in a novel form appropriate fo r direct classical correspondence. The classical impulse cross section is t hen uniquely defined and yields the first general classical expression for nl - n'l' collisional transitions. The derived cross sections satisfy the o ptical theorem and detailed balance. Direct connection with the classical b inary encounter approximation is also firmly established. The unified metho d introduced is general in its application to various collision and recombi nation processes and enables new directions of enquiry to be pursued quite succinctly.