Atomic-structure effects in multiphoton ionization of magnesium

We present an application of a simple configuration-interaction approach to multiphoton ionization of magnesium, using a finite ${\mathit{L}}^2$-basis set constructed from a nearly complete set of one-particle frozen-core Hartree-Fock orbitals. The effects due to multielectron interactions to two- and three-photon processes at energies both near and away from the resonant structures dominated by singly excited intermediate states and doubly excited autoionization states are examined in detail. Our calculation has shown that the multiphoton spectra are mostly dominated by the resonant structures due to intermediate singly excited bound states. Such spectra are qualitatively different from the single photoionization spectrum, which often exhibits a strong presence of doubly excited autoionization structures. Our calculated results are in close agreement with other existing experimental and theoretical results for single- and two-photon ionizations.