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 Ar+2 and Kr+2, the observed structure is tentatively assigned to 1u (1Πu) and O+u (1Σu+) states which correlate with the ‘‘promoted’’ ndπg and ndσg series. Plausible assignments for the trimer spectra are also discussed.