We develop a projection-operator theory of photodisintegration. It is shown that the coupling of 3p-3h (three-particle, three-hole) modes to the 1p-1h modes can explain the intermediate structure of the giant resonance in oxygen when the 1p-1h states are treated as "doorways" for $\gamma$-ray absorption and for particle emission. The structure problem is treated using the interacting-boson approximation of Iachello and Feshbach.

• Received 16 February 1971

DOI:https://doi.org/10.1103/PhysRevLett.26.902