Journal ArticleObservation of an Electric Quadrupole Transition in a Negative Ion: Experiment and TheoryWalter, C. W.; Spielman, S. E.; Ponce, R.; Gibson, N. D.; Yukich, J. N.; Cheung, C.; Safronova, M. S.null2021-02-0110284173Physical Review Letters12680031-9007https://doi.org/10.1103/PhysRevLett.126.0830011707743National Science Foundation