Fe b 20 11 On highly accurate calculations of the excited n 1 S ( L = 0 ) − states in helium atoms

The total energies and various bound state properties of the excited 21S(L = 0)−states in two-electron helium atoms, including the ∞He, 4He and 3He atoms, are determined to very high numerical accuracy. The convergence of the results obtained for some electron-nuclear and electronelectron expectation values and, in particular, for the electron-nuclear and electron-electron cusp values, is discussed. The field component of the isotope shift and lowest order QED correction are estimated for the 21S(L = 0)−states in the 4He and 3He atoms. We also apply our highly accurate methods to numerical computations of the excited n1S−states (for n = 3 and 4) in two-electron atomic systems. PACS number(s): 31.15.ac, 31.15.ae and 31.30.Gs E–mail address: [email protected] E–mail address: [email protected]