Lifetimes of Some Doubly Excited Levels in Neutral Helium

Abstract

We have searched for radiative transitions from doubly excited levels in He I, using the beam-foil method. The spectra showed the $1s2p{}_{}{}^3{}_{}{}^{}P-2p^2{}_{}{}^3{}_{}{}^{}P$ transition at 320. 4 Å and some weaker lines, which are also interpreted as transitions from the doubly excited system. Radiative lifetimes were measured for three lines. Our value for the $2p^2{}_{}{}^3{}_{}{}^{}P$ level, 0.080 ± 0.007 nsec, is in agreement with the recent theoretical value of 0.0803 nsec. The possibilities of observing transitions from doubly excited levels in the He I isoelectronic sequence are briefly discussed.