The first direct experimental observation of an electric quadrupole ($E2$) absorption transition between bound states of an atomic negative ion has been made. The transition was observed in the negative ion of bismuth by resonant ($1+1$) photon detachment from ${\mathrm{Bi}}^{-}$ via ${}^3{P}_2\to {}^3{P}_0$ excitation. The $E2$ transition properties were completely independently calculated using a hybrid theoretical approach to account for the strong multilevel electron interactions and relativistic effects. The experimental and ab initio theoretical results are in excellent agreement, providing valuable new insight into this complex system and forbidden transitions in negative ions more generally.

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负离子中电四极跃迁的观察：实验和理论

电四极杆的首次直接实验观测（$E\mathrm{2个}$）已经在原子负离子的键合态之间进行了吸收跃迁。通过共振在铋的负离子中观察到跃迁（$\mathrm{1个}+\mathrm{1个}$）从 ${双}^{-}$ 通过 ${}^3{P}_{\mathrm{2个}}\to {}^3{P}_0$励磁。这$E\mathrm{2个}$过渡性质是完全独立地使用混合理论方法计算的，以解决强多级电子相互作用和相对论效应。实验结果和从头算的理论结果非常吻合，这为该复杂系统提供了有价值的新见解，并且更广泛地禁止了负离子的跃迁。