Inner-valence shell photoionization of Ar₂, Ar₃, Kr₂, and Kr₃

The inner-valence shell photoionization spectra (420 <λ <500 Å) of Ar₂, Ar₃, Kr₂, and Kr₃ have been obtained with a molecular beam apparatus using synchrotron radiation from the VUV storage ring at the National Synchrotron Light Source. The photoionization spectra exhibit regular series of window resonances which are closely associated with the ms→np Rydberg series in atomic Ar(m = 3) and Kr(m = 4). Vertical ionization potentials of the lowest ionic state in the molecular ms regions were obtained by series extrapolation and these were used to estimate the well depths in the Franck-Condon region and dissociation energies. Assignments of the observed Rydberg transitions were made by analogy with similar excitations in He₂ and the group II and II B metal dimers. For Ar₂⁺ and Kr₂⁺, the observed structure is tentatively assigned to 1_u ( ¹Π_u) and O_u⁺ ( ¹Σ_u⁺) states which correlate with the "promoted" ndπ_g and ndσ_g series. Plausible assignments for the trimer spectra are also discussed.