We have measured the radiative lifetimes of the 4<i>S</i>, 4<i>D</i>, 4<i>F</i>, 5<i>S</i>, 5<i>P</i>, 5<i>D</i>, and 5<i>F</i> states in singly ionized helium using the high-energy atomic-beam technique. The measured values of the lifetimes are in excellent agreement with those calculated for hydrogenic atoms. Extensions of the experimental technique to the measurement of excitation cross sections and fine-structure splittings are discussed.
J. A. JORDAN, JR., G. S. BAKKEN, and R. E. YAGER, "Radiative Lifetimes of Some n = 4 and n = 5 States in He II," J. Opt. Soc. Am. 57, 530-534 (1967)