New values for someHe4I1snlenergy levels, ionization energies, and Lamb shifts

Abstract

Recent experimental determinations of energy separations within the $1snl$ term system ($n=2\ensuremath{-}6$) have been used to reevaluate 35 levels. Most of the levels have estimated errors less than 0.001 ${\mathrm{cm}}^{\ensuremath{-}1}$ relative to the $2 ^{3}P$ levels. Addition of accurate theoretical term values (ionization energies) available for several $1snl$ levels to the corresponding experimental level values gives generally consistent values for the principal ionization energy (${E}_{I}$). The theoretical energies are further confirmed by the agreement of the weighted average of seven of these ${E}_{I}$ values with a value obtained by fitting Ritz formulas to three accurately determined $1snl$ series; the suggested new ${E}_{I}$ is 198 310.7745(40) ${\mathrm{cm}}^{\ensuremath{-}1}$ on an energy scale fixed by the value 171 135.0000 ${\mathrm{cm}}^{\ensuremath{-}1}$ for $2 ^{1}P$. Lamb shifts are derived for the $2$, $3$, $4 ^{3}S_{1}$, $2 ^{1}S_{0}$, $2 ^{3}P_{1}$, and $2 ^{1}P_{1}$ levels as differences between experimental term values obtained with the new ${E}_{I}$ and corresponding calculated term values not including Lamb shifts. The experimental and calculated values for the ${1s}^{2} ^{1}S_{0}$ ground level relative to the present $1snl$ excited-level system are 0.00\ifmmode\pm\else\textpm\fi{}0.15 and 0.073\ifmmode\pm\else\textpm\fi{}0.009 ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively, so that a \ensuremath{\sim}20-fold increase in the experimental accuracy would be required to test the calculated ground-level Lamb shift.