Correction to then P 13Levels of the Helium Isoelectronic Sequence Owing to Mixing with then P 11State

The contribution to the $n {}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ ionization energy owing to mixing with the $n {}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state has been computed for the $2 {}_{}{}^3{}_{}{}^{}P$ to $5 {}_{}{}^3{}_{}{}^{}P$ states of the helium isoelectronic sequence up to $Z=10\mathrm{}$. Corrected values for the fine-structure splittings of these levels are listed. The theoretical and experimental values for the $2 {}_{}{}^3{}_{}{}^{}S_{ 1}^{}{}_{}{}^{}-2 {}_{}{}^3{}_{}{}^{}P_{ 1}^{}{}_{}{}^{}$ energy difference are found to be in good agreement provided that the $2 {}_{}{}^1{}_{}{}^{}P_{ 1}^{}{}_{}{}^{}$ mixing correction to the $2 {}_{}{}^3{}_{}{}^{}P_{ 1}^{}{}_{}{}^{}$ level and an estimate of the Lamb-shift correction to the $2 {}_{}{}^3{}_{}{}^{}S_{ 1}^{}{}_{}{}^{}$ energy are included in the calculation.