Double photoionization of argon into the 3s3p 5 1 P- and3 P-states

Double photoionization of argon was studied by photon induced fluorescence spectroscopy (PIFS). Cross sections for the double photoionization into the 3s3p ^{5 1} P,³ P states of Ar⁺⁺ are presented for exciting photon energies between threshold and 120 eV. In the threshold range the energy dependencies of these cross sections were determined for the first time. Singlet and triplet states are populated with comparable probabilities at equal excess energies, in contrast to predictions of the extended Wannier theory. Athv=100 eV the spin-or-bit splitting of the 3s3p ^{5 3} P state was resolved, and a cross section for the production of Ar⁺⁺ 3s ⁰3p ^{6 1} S ₀ was determined for the first time.