Accurate Wavelength Measurement of the 1s2pP∘3−2p2P3 Transition in He4 I

An accurate spectroscopic measurement has yielded 320.2926 \ifmmode\pm\else\textpm\fi{} 0.0010 \AA{} for the wavelength of the $1s2p^{3}P^{\ensuremath{\circ}}\ensuremath{-}2{p}^{2}^{3}P$ transition in $^{4}\mathrm{He}$ I. Combining this wavelength with the well-known position of the $1s2p$ term gives an experimental value of 481 301.5 \ifmmode\pm\else\textpm\fi{} 1.2 ${\mathrm{cm}}^{\ensuremath{-}1}$ for the position of the doubly excited $2{p}^{2}^{3}P$ term relative to the ground $1{s}^{2}^{1}S$. The new measurement is in excellent agreement with Aashamar's theoretical calculation of 481 301.6 ${\mathrm{cm}}^{\ensuremath{-}1}$ for the energy of the term.