Potvliege, RM., & Joachain, CJ. (1985). Coherent Electron-impact Excitation of the N = 2 States of Atomic-hydrogen At Intermediate Energies. Journal of Physics B: Atomic, Molecular and Optical Physics, 18(16), L585-L588. https://doi.org/10.1088/0022-3700/18/16/009 (Original work published 1985)