Complete two-electron spectra in double photoionization: the rare gases Ar, Kr, and Xe.

A new spectroscopic technique, giving complete two-dimensional e(-)-e(-) coincidence spectra in single photon double photoionization, is presented. The technique resolves the states of doubly charged ions and provides spectra of the individual electrons emitted in formation of each final dication state. Complete spectra for double photoionization of Xe, Kr, and Ar at photon energies up to 51 eV have been recorded. Overall and surprisingly, the np(4) 3P, 1D, and 1S states are populated according to their statistical weights. When the evident autoionization is excluded, the supposedly favored 3P states are in fact disfavored. Detailed information on the autoionization processes is also made available.