Tensorial form and matrix elements of the relativistic nuclear recoil operator

Within the lowest-order relativistic approximation (similar to v(2)/c(2)) and to first order in m(e)/M, the tensorial form of the relativistic corrections of the nuclear recoil Hamiltonian is derived, opening interesting perspectives for calculating isotope shifts in the multiconfiguration Dirac-Hartree-Fock framework. Their calculation is illustrated for selected Li-, B- and C-like ions. This work underlines the fact that the relativistic corrections to the nuclear recoil are definitively necessary for obtaining reliable isotope shift values.