Role of initial-state electron correlation in one-photon double ionization of atoms and molecules

Abstract

By decomposing the initial state wave function into its unique natural orbital expansion, as defined in the 1950s by Löwdin and used in modern studies of entanglement, we analyze the role of electron correlation in the initial state of an atom or molecule in determining the angular distribution of onephoton double ionization. Final state correlation of the two ejected electrons is treated completely in numerically accurate calculations as the initial states of He, H − and H2 are built up from correlating configurations in strict order of decreasing natural orbital occupations. In the two-electron atoms it is found that the initial state correlation plays a sometimes modest but generally measurable role. In striking contrast, for H2 a large number of correlating configurations in the ground state is often necessary to produce angular distributions even approximately resembling the correct ones. One-photon double photoionization of oriented H2 is found to be particularly sensitive to left-right correlation along the bond.

Two-photon double photoionization of atomic Mg by ultrashort pulses: Variation of angular distributions with pulse length

“…Specifically, for magnesium there are more prominent contributions from excited orbitals (3p, 4s, 3d, etc.) that are both energetically closer to the valence 3s orbital and also possess more complex nodal structure than is the case for helium, where the 1s 2 configuration is substantially dominant and composed of orbitals that are largely separated energetically from the excited orbitals constituting the correlating configurations [42]. For the pulse lengths considered, the observed complicated angular distributions at these modest photon energies in Mg can be attributed to the greater significance of the correlating contributions comprising the initial state, in addition to the fact that these excited contributions more prominently feature nearby orbitals that have a richer radial and angular structure than those which are analogous in correlating configurations of helium (2s, 2p, etc.…”

Strong-field-induced single and double ionization dynamics from single and double excitations in a two-electron atom

“…The effects of strong NIR fields on the electron dynamics, in this context, have been typically studied starting from the ground state influenced by a single NIR laser pulse [19,20] or a combination of an NIR and a time-delayed extreme ultraviolet (XUV) pulse, as in TAS [23][24][25]. One-and few-photon double ionization of helium has also been investigated under the influence of intense XUV fields, where couplings between the ground state and single and double excitations were observed [26,27].…”