Analysis of correlations between dipole transitions 1 1 − → 0 1 + and 3 1 − → 2 1 + based on the collective model

The purpose of the work is to evaluate effect of the isovector dipole and quadrupole-octupole modes coupling on the $B(E1;1^-_1\rightarrow 0^+_1)/B(E1;3^-_1\rightarrow 2^+_1)$ ratio. The Hamiltonian of the phenomenological collective model is used to calculate mixing of the isovector dipole and quadrupole and octupole modes. The effect of the admixture of the giant dipole resonance to the low-lying collective quadrupole and octupole modes is estimated. It is shown that the coupling of the quadrupole and octupole collective modes to giant dipole resonance leads to decrease of the ratio $B(E1;1^-_1\rightarrow 0^+_1)/B(E1;3^-_1\rightarrow 2^+_1)$ relative to the value 7/3 predicted by the pure collective quadrupole-octupole model.