A quantum-mechanical method for calculating level widths and shifts, applicable to type I unimolecular predissociation

A quantum mechanical approach to type I unimolecular predissociation is developed in terms of Feshbach's optical potential. The resulting method is formally applicable to many cases of molecular breakup caused by the crossing of coupled bound and dissociative electronic surfaces. These include cases in which multiple bound and/or dissociative channels are accessible. There are two restrictions : (1) coupling among dissociative channels should be negligible, and (2) only two product fragments are allowed, of fixed atomic composition regardless of internal state. A harmonic oscillator coupled to a dissociative infinite-step or hard-sphere potential is used in comparing the usual perturbation theory results to the present approach.