Photoionization of an atom in the presence of a uniform static electric field
provides the unique opportunity to expand and visualize the atomic wave
function at a macroscopic scale. In a number of seminal publications dating
back to the 1980s, Fabrikant, Demkov, Kondratovich, and Ostrovsky showed that
this goal could be achieved by projecting slow (meV) photoionized electrons
onto a position-sensitive detector and underlined the distinction between
continuum and resonant contributions. The uncovering of resonant signatures
was achieved fairly recently in experiments on the nonhydrogenic lithium atoms
[Cohen et al., Phys. Rev. Lett. 110, 183001 (2013)]. The purpose of the
present article is the general description of these findings, with emphasis on
the various manifestations of resonant character. From this point of view,
lithium has been chosen as an illustrative example between the two limiting
cases of hydrogen, where resonance effects are more easily identified, and
heavy atoms like xenon, where resonant effects were not observed
