α4R corrections to singlet states of helium

Corrections of order alpha R-4 are calculated for the singlet states 1 S-1(0) and 2 S-1(0) of the helium atom. The result for the 1 S-1(0) state is in slight disagreement with that of Korobov and Yelkhovsky [Phys. Rev. Lett. 87, 193003 (2001)]. The results obtained lead to a significant improvement of the transition frequencies between low-lying levels of the helium atom. In particular theoretical predictions for the 2 S-1(0)-1 S-1(0) transition are found to be in disagreement with experimental values.