Photoelectron spectra of Ar2 and Kr2 and dissociation energies of the rare gas dimer ions

Abstract

The photoelectron spectra of Ar2 and Kr2 were determined at 584 Å with resolutions of 18 and 21 meV, respectively, using an apparatus which combines a supersonic molecular beam source with a hemispherical photoelectron spectrometer. Dissociation energies were determined for the weakly bound B 2Π(3/2)g and C 2Π(1/2)u excited states of the dimer ions, and were found to average approximately 30% greater than those predicted by recent theoretical calculations. Optimum potentials were determined for the Ar+2 and Kr+2 ground states by fitting calculated Franck–Condon distributions to the observed photoelectron peaks. As in the case of Xe+2, the optimum Rg+2 potentials retain the shapes determined by theoretical calculations, but they are modified by scaling their dissociation energies to the experimentally determined values. The Morse function is shown to be an inadequate potential form for the Rg+2 ground states, since it is too attractive at large internuclear distance.