Fragmentation of the two-octupole phonon multiplet in 208Pb

The properties of the lowest two-phonon states in Pb-208 built On the collective octupole vibration are studied within the quasiparticle phonon model. Calculations including up to three-phonon coupling yield a strong fragmentation of the 6(+) member of the multiplet, explaining the failure of recent heavy ion Coulomb excitation experiments used to observe this state. Some splitting of the 2(+) strength is predicted while the 0(+) and 4(+) members remain relatively pure. The present results also question the proposed signature for the two-octupole states of enhanced El decays to one-phonon states. [S0031-9007(98)08236-2].