R.
Ponce
Walter, C. W., Spielman, S. E., Ponce, R. ., Gibson, N. D., Yukich, J. N., Cheung, C. ., & Safronova, M. S. (2021). Observation of an Electric Quadrupole Transition in a Negative Ion: Experiment and Theory. Physical Review Letters, 126. http://doi.org/10.1103/PhysRevLett.126.083001