Effect of the spin-orbit interaction in photoionization Stark spectra ofml=1excited rubidium atoms

Experimental results on the photoionization spectra of excited rubidium atoms in a well-defined $m_l=1\mathrm{}$ state in the presence of an electric field are reported. Spectra corresponding to a definite polarization of the ionizing light exhibit characteristic resonances which are ascribed either to the non-Coulombic part of the central potential or to the spin-orbit interaction. The different line profiles are interpreted as being due to interferences between discrete states and continua, the observed structures depending directly on the density of oscillator strengths and not simply on the density of continuum states.