CORRECTIONS OF ORDER $α^2(Zα)^5$ TO HYPERFINE SPLITTING AND LAMB SHIFT

Corrections to hyperfine splitting and Lamb shift of order $\alpha^2(Z\alpha)^5$ induced by the diagrams with radiative photon insertions in the electron line are calculated in the Fried-Yennie gauge. These contributions are as large as $-7.725(3)\alpha^2(Z\alpha)^5/(\pi n^3)(m_r/m)^3m$ and $-0.6711(7)\alpha^2(Z\alpha)/(\pi n^3)E_F$ for the Lamb shift and hyperfine splitting, respectively. Phenomenological implications of these results are discussed with special emphasis on the accuracy of the theoretical predictions for the Lamb shift and experimental determination of the Rydberg constant. New more precise value of the Rydberg constant is obtained on the basis of the improved theory and experimental data.