Effects of anharmonic vibration on large-angle quasi-elastic scattering of ¹⁶O+¹⁴⁴Sm

We study the effects of double octupole and quadrupole phonon excitations in the ¹⁴⁴Sm nucleus on quasi-elastic ¹⁶O+¹⁴⁴Sm scattering at backward angles. To this end, we use the coupled-channels framework, taking into account explicitly the anharmonicities of the vibrations. We use the same coupling scheme as that previously employed to explain the experimental data of sub-barrier fusion cross sections for the same system. We show that the experimental data for the quasi-elastic cross sections are well reproduced in this way, although the quasi-elastic barrier distribution has a distinct high energy peak which is somewhat smeared in the experimental barrier distribution. We also discuss the effects of proton transfer on the quasi-elastic barrier distribution. Our study indicates that the fusion and quasi-elastic barrier distributions for this system cannot be accounted for simultaneously with the standard coupled-channels approach.