The lifetimes of the metastable $1s2s2p{\hspace{0.5em}}^4{P}_{5/2}$ level of ${\mathrm{He}}^{-},$ as well as the lifetime of the average of the ${}^4{P}_{3/2}$ and ${}^4{P}_{1/2}$ levels, have been measured using a new type of ion trap that stores keV ion beams using electrostatic fields only. The use of a pure electrostatic field avoids the complication of magnetic-field-induced mixing effects, which can interfere with the measurement of the spontaneous decay. The measured lifetime for the ${}^4{P}_{5/2}$ state, after correction for decay induced by blackbody radiation, is $343\pm 10\hspace{0.5em}\mu \mathrm{s}.$ This value is consistent with previous experiments, and in excellent agreement with the most recent theoretical calculations. The average lifetime of the ${}^4{P}_{3/2}$ and ${}^4{P}_{1/2}$ is $8.9\pm 0.2\hspace{0.5em}\mu \mathrm{s},$ which is about 20% lower than the weighted theoretical value.

• Received 8 September 1998

DOI:https://doi.org/10.1103/PhysRevA.59.267