Conventionally, octupole deformation in nuclei has been attributed to strong $\mathrm{\Delta }l=3$ couplings between opposite-parity single-particle orbitals. In this work, we demonstrate that the often-overlooked $\mathrm{\Delta }l=1$ mode also plays an important role. Taking orbitals near the octupole magic number $N=134$ as a benchmark, we systematically evaluate the $\mathrm{\Delta }l=1$ and $\mathrm{\Delta }l=3$ mixing ratios of the wave functions within the Nilsson model. We introduce component-resolved single-particle octupole energy contributions, based on the Hellmann-Feynman relation, to quantify the contributions of each $(\mathrm{\Delta }l,\mathrm{\Delta }j)$ coupling. Furthermore, the impact of $\mathrm{\Delta }l=1$ coupling on the rotational structure is demonstrated via particle-rotor model calculations for ${}^{221}\mathrm{Ra}$ and ${}^{223}\mathrm{Th}$. Our work suggests that $\mathrm{\Delta }l=1$ and $\mathrm{\Delta }l=3$ octupole couplings act synergistically in driving reflection asymmetry, necessitating a revised paradigm for understanding octupole correlation.

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• Collective levels
• Nuclear shapes and moments
• A ≥ 220
• Collective models