Computation of the ac Stark effect in the ground state of atomic hydrogen

Using a Sturmian function expansion we have computed the nth order coefficients En(), for 2n22, in the perturbation expansion of the ac Stark effect in the hydrogen 1s state. An effective convergence similar to that in the dc case is observed. A parametrization of these coefficients, based upon the analytic structure of the Coulomb Greens function, separates the rapid oscillatory resonant behavior and the smooth background variation with respect to.