Ln. Labzowsky et Ma. Tokman, REFERENCE STATE CONTRIBUTIONS TO THE 2-PHOTON INTERACTION CORRECTIONSFOR THE ENERGY SHIFTS IN MULTICHARGED FEW-ELECTRON IONS, Journal of physics. B, Atomic molecular and optical physics, 28(17), 1995, pp. 3717-3727
The second-order cr corrections in QED, in particular the two-photon e
xchange corrections, are investigated by the line profile approach. Th
e expressions for equal-energy 'reference state' corrections and for t
he unequal-energy Coulomb-transverse corrections are given. The numeri
cal calculations for the latter corrections of 'box' and 'cross' type
in the case of (1s(1/2))(2)2s(1/2) and (1s(1/2))(2)2p(1/2) states of L
i-like heavy ions are presented.